InlineEdit: Support 'go to line' command

Inline edit currently uses the default key map and doesn't provide any
means to jump to a specific line. Feature request to add this to the
core was rejected: [1].

There is addon in the wild that does just that: [2]. But the request
to clarify the license for this feature remained unanswered: [3].

Add un ugly prompt dialog and bind it to 'Ctrl+L' and 'Cmd+L' keys.

[1] https://github.com/codemirror/CodeMirror/issues/3030
[2] https://github.com/djadmin/djadmin.github.io/blob/master/addon/search/goto-line.js
[3] https://github.com/djadmin/djadmin.github.io/commit/6ee5941512d73cdcede929b6b832896842e0845d#diff-5

Change-Id: Ia9de2003531a10b256f5fb6cedeead2aaff2fd79