Auto-Paste Functionality via Keyboard Shortcuts

[neocotic]

Same as #95, but auto-pastes a template to a input field/textarea when it was focused by the user while using a keyboard shortcut to access the template.

[neocotic]

Attempt to find focused UI component using document.querySelector(':focus').

[neocotic]

I've tested this again after fixing a bug and I'm happy with the results. That said; it's worth noting the following additional changes to keyboard shortcuts;

• They now have an independent section in the Options page
• Content scripts are now kept up-to-date with those in use and only send requests to the controller for active hotkeys
• Event.preventDefault is called when triggered by an input/textarea element (preventing accent characters being inserted - again, only done when active hotkeys are detected)
• Event listener is now bound to keydown instead of keyup