[Web] Fat-finger language modeling

[LMLayer] The ModelCompositor

[ios] fix crash when there  is no model to download

[Android] Download lexical models via menu

[LMLayer, Android] Adds workaround for Android duplicate load msg bug.

[LMLayer] Trie model: Replace the prefix with the suggestion

* Default keyboard doesn't have "custom keyboard" setting so read it as optional parameter
* Don't notify "KEYBOARD_DOWNLOAD_FINISHED" when only downloading lexical model
* Removed registration of lexical model upon download (complications with async task)

[developer] Lexical model compiler was not flattening languages arrays for .model_info file

[Developer] Lexical model compiler should validate model ids found in packages while building

The activity is a background activity so it can't change the WebView height when registering the model

Also fix deleteLexicalModel to not use modelKey
(Sencoten key has mix of `-` and `_` in the language ID and model ID)

[developer] Fixes #1793. Lexical model compiler was not flattening languages arrays for .model_info file

* Fix determination of custom keyboard from package
* Add Toast notification when re-installing a lexical model.

[LMLayer] Deselect suggestions when one is selected.