Improve "Export Layout" button interactions:

- Do not mark "Export Layout" button as disabled in the .html, only
  disable it after changes to the layout have been made.

- Trigger "modified.layout" event on column size changes.
Include bootstrap .disabled styles so the disabled state of the "Export Layout" button is visible.
Improve css style of Export Layout dialog.
Add cover-(type)-tile class to all tile templates.

This addresses the issue #189 for all the default tiles, but doesn't do it automatically for new tiles.
Merge remote-tracking branch 'upstream/master' into issue_189

* upstream/master:
  Fix some JSHint warnings on JS files
  Add message on template for empty carousel and enhance testing
  Add test for feature and line in change log (CC @rristow)
  Add/Removed the respective css-marker when the layout is edit/saved; Removed alert
  Warning to save when leaving layout tab

Conflicts:
	src/collective/cover/tiles/templates/carousel.pt
Merge pull request #327 from warpr/issue_306

Issue 306
Merge pull request #329 from warpr/export_layout_dialog_style

Improve css style of Export Layout dialog.
Update tests for the css class changes made in commit b52d5576a8cf2833ba7e05d73607606e7cce0954.
Make the test_file_tile.robot test more reliable.

This test failed occasionally on my development machine, with this change it seems to
be more reliable.
Support text from Dexterity items for the bodycontent and richtext tiles.

Fixes #323.
Robot tests: reload the compose page before editing again.

Should fix even more spurious test failures.
Use "Wait until .." and use id attributes when clicking some buttons in the robot tests.

This seems to make these more reliable, as they otherwise occasionally fail.
Robot tests: reload the compose page once more.

During some test runs this is needed, during others not.
Merge pull request #328 from warpr/issue_189

Add cover-(type)-tile class to all tile templates.
Bump up version of Selenium browser (refs. #332)

* version 2.36.0 fixes drag and drop by offset behaviour
* version 2.37.0 repackages with fix for Firefox native events on Linux

Let's pray!
Remove expected failure tag as RF test is passing again
Skip carousel tile RF test failing apparently because a Selenium regression

* Fixes #332
* Refs. #333
Merge branch 'master' into issue-305