Improve "Unchanged String" view
* Fixed styling of first row of results
* Make column headers visible even when a component is filtered
* Added dir and lang attributes to rows

"Unchanged strings" model:
* Don't try to compare non existing strings

Fixed undefined var $target_string2 warning in views/results_entities.php
Use htmlentities on search strings before displaying them, improve CSS for no results
Issue #400: add github pushes integration hook

Action needed on the beta server after this push:
- add secret key in config.ini
- create a file web/github_log.txt with the user www-data:www-data

We don't keep the log file in app/logs/ because we want to be able to access the date of the last update from GitHub into the browser
Merge pull request #401 from pascalchevrel/issue400-update_beta_site_with_github_pushes

Issue #400: add github pushes integration hook
Merge pull request #398 from flodolo/issue397

Encode HTML on search string before display, improve CSS without results
Merge pull request #395 from flodolo/fix_unchanged

Improve "Unchanged String" view