add additional languages to .travis.yml
Add additional shortcuts

add shortcut Ctrl+T for "Insert Table" and Ctrl+G for "Insert Image" menu
item.
Add shortcut Ctrl+Q for menu item "Blockquote"
Make edit commands usable without selection (#75)

Make the edit commands "Strong", "Emphasize", "Strikethrough" and "Inline
Code" usable without an selected text in the markdown editor.

Fixes #75
Improve usability of edit command "Blockquote"

The edit command "Blockquote" now also supports to mark several selected
lines as blockquote.