improve usability: add shortcuts for compose/send new toot [#505]

[unstabler]

https://twingyeo.kr/@cheesekun/102184993516052526

sorry for my bad english > <);

[connyduck]

In MainActivity, there is already code that handles key events. Can we merge the existing code with you new code somehow?

[unstabler]

um.. i think onKeyDown will be called for each key event. (ctrl + enter raises onKeyDown(ctrl) onKeyDown(enter) twice)
so i used onKeyShortcut instead to handle multiple-key event > <);

[connyduck]

yes, I understand that, but can you move the code from onKeyDown to onKeyShortcut and see if it still works?

[unstabler]

omg it still works! :0

[connyduck]

Ok, I meant the other way round, but this is also fine. Thank you!