Rework backend add MQTT and WebSocket support

* Update back end to add MQTT and WebSocket support
* Update demo project to demonstrate MQTT and WebSockets
* Update documentation to describe newly added and modified functionallity
* Introduce separate MQTT pub/sub, HTTP get/post and WebSocket rx/tx classes
* Significant reanaming - more accurate class names
* Use PROGMEM_WWW as default
* Update README documenting PROGMEM_WWW as default
* Update README with API changes

interface/src/security/ManageUsersForm.tsx

@@ -154,11 +154,13 @@ class ManageUsersForm extends React.Component<ManageUsersFormProps, ManageUsersF
           </Table>
           {
             this.noAdminConfigured() &&
-            <Typography component="div" variant="body1">
+            (
               <Box bgcolor="error.main" color="error.contrastText" p={2} mt={2} mb={2}>
-                You must have at least one admin user configured.
+                <Typography variant="body1">
+                  You must have at least one admin user configured.
+                </Typography>
               </Box>
-            </Typography>
+            )
           }
           <FormActions>
             <FormButton startIcon={<SaveIcon />} variant="contained" color="primary" type="submit" disabled={this.noAdminConfigured()}>

interface/src/security/SecuritySettingsForm.tsx

@@ -33,11 +33,11 @@ class SecuritySettingsForm extends React.Component<SecuritySettingsFormProps> {
           onChange={handleValueChange('jwt_secret')}
           margin="normal"
         />
-        <Typography component="div" variant="body1">
-          <Box bgcolor="primary.main" color="primary.contrastText" p={2} mt={2} mb={2}>
+        <Box bgcolor="primary.main" color="primary.contrastText" p={2} mt={2} mb={2}>
+          <Typography variant="body1">
             If you modify the JWT Secret, all users will be logged out.
-          </Box>
-        </Typography>
+          </Typography>
+        </Box>
         <FormActions>
           <FormButton startIcon={<SaveIcon />} variant="contained" color="primary" type="submit">
             Save