Fixes for PR 59 (Helix)

Hey - I've been using Amber with PR 59 (Helix support) for a few days now and I've spotted a few issues with it.

I'm PR'ing to your fork, helix branch, so that my fixes will be automatically added to the pull request.

Please do note that you don't actually want to _merge_ this PR, but rather "import" my commits into your local branch and then push to GitHub. (You can technically merge the PR on GitHub, but then you have to remove the merge commit after and force-push to GitHub.)

A big thanks to Joe, the guy from the original PR, for his work.

Details (so that you can also link this PR to pecinko):
* DialogContentSettings: Joe changed the element IDs, but forgot to also change them in on* actions. The result was that It was impossible to modify a source;
* DialogAddonInfo: just a cosmetic change, to avoid confusion;
* DialogKeyboard: this was driving me crazy. Moving from one button to another was frequently selecting the wrong one (i.e. moving down from K would go to V instead of U);
* DialogMediaSource: moving on the left from the edit control for the source name should go to OK, not Cancel;
* DialogProgress, DialogOK, DialogYesNo: third line was cut;
* DialogContextMenu: fixed width for some languages where the translated text is longer;
* Includes_Variables: when browsing through movies, the "Details" line for movie sets had an additional separator. I've just moved the separator to make it conditional, so that only properties with actual content show a separator. Fixes: `2013 * * 8.1` -> `2013 * 8.1`;
* Includes: this fixes the issue I have reported in PR 59 about DialogVideoInfo being crazy-aligned. Also fixed widths for some languages where the translated text is longer. From what I can tell, it seems to match this screenshot pretty well: https://raw.githubusercontent.com/pecinko/skin.amber/master/_screenshots/screenshot05.jpg - but I've never used Amber on Gotham and I don't have a Gotham setup to test.