Allow features to be disabled at build time (#143)

* Add framework for built-time feature selection
* Allow MQTT, NTP, OTA features to be disabled at build time
* Allow Project screens to be disabled at build time
* Allow security features to be disabled at build time
* Switch to std::function for StatefulService function aliases for greater flexibility
* Bump various UI lib versions
* Update docs

interface/src/features/ApplicationContext.tsx

@@ -0,0 +1,23 @@
+import React from 'react';
+import { Features } from './types';
+
+export interface ApplicationContext {
+  features: Features;
+}
+
+const ApplicationContextDefaultValue = {} as ApplicationContext
+export const ApplicationContext = React.createContext(
+  ApplicationContextDefaultValue
+);
+
+export function withAuthenticatedContexApplicationContext<T extends ApplicationContext>(Component: React.ComponentType<T>) {
+  return class extends React.Component<Omit<T, keyof ApplicationContext>> {
+    render() {
+      return (
+        <ApplicationContext.Consumer>
+          {authenticatedContext => <Component {...this.props as T} features={authenticatedContext} />}
+        </ApplicationContext.Consumer>
+      );
+    }
+  };
+}

interface/src/features/FeaturesContext.tsx

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+import React from 'react';
+import { Features } from './types';
+
+export interface FeaturesContext {
+  features: Features;
+}
+
+const FeaturesContextDefaultValue = {} as FeaturesContext
+export const FeaturesContext = React.createContext(
+  FeaturesContextDefaultValue
+);
+
+export interface WithFeaturesProps {
+  features: Features;
+}
+
+export function withFeatures<T extends WithFeaturesProps>(Component: React.ComponentType<T>) {
+  return class extends React.Component<Omit<T, keyof WithFeaturesProps>> {
+    render() {
+      return (
+        <FeaturesContext.Consumer>
+          {featuresContext => <Component {...this.props as T} features={featuresContext.features} />}
+        </FeaturesContext.Consumer>
+      );
+    }
+  };
+}

interface/src/features/FeaturesWrapper.tsx

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+import React, { Component } from 'react';
+
+import { Features } from './types';
+import { FeaturesContext } from './FeaturesContext';
+import FullScreenLoading from '../components/FullScreenLoading';
+import ApplicationError from '../components/ApplicationError';
+import { FEATURES_ENDPOINT } from '../api';
+
+interface FeaturesWrapperState {
+  features?: Features;
+  error?: string;
+};
+
+class FeaturesWrapper extends Component<{}, FeaturesWrapperState> {
+
+  state: FeaturesWrapperState = {};
+
+  componentDidMount() {
+    this.fetchFeaturesDetails();
+  }
+
+  fetchFeaturesDetails = () => {
+    fetch(FEATURES_ENDPOINT)
+      .then(response => {
+        if (response.status === 200) {
+          return response.json();
+        } else {
+          throw Error("Unexpected status code: " + response.status);
+        }
+      }).then(features => {
+        this.setState({ features });
+      })
+      .catch(error => {
+        this.setState({ error: error.message });
+      });
+  }
+
+  render() {
+    const { features, error } = this.state;
+    if (features) {
+      return (
+        <FeaturesContext.Provider value={{
+          features
+        }}>
+          {this.props.children}
+        </FeaturesContext.Provider>
+      );
+    }
+    if (error) {
+      return (
+        <ApplicationError error={error} />
+      );
+    }
+    return (
+      <FullScreenLoading />
+    );
+  }
+
+}
+
+export default FeaturesWrapper;

interface/src/features/types.ts

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+export interface Features {
+  project: boolean;
+  security: boolean;
+  mqtt: boolean;
+  ntp: boolean;
+  ota: boolean;
+}