fix(collapse): unregisters collapse toggles/targets when they are destroyed

When the bsCollapseTarget/bsCollapseToggle elements were destroyed, the internal control arrays in bsCollapse were not being updated, which caused invalid index values for current active item.
fix(scrollSpy) destroy scroll event handler
feat(select): allow select all/none button labels to be changed

This provides 2 new options, 'allText' and 'noneText', that allow setting the text to display on the corresponding buttons. These options can be set by changing the provider defaults or by using data attributes on the select element.

Fixes #1364
docs(navbar): fix navbar plunker demo
feat(date and time picker): add unix time support

Type 'unix' supports value to be in seconds (unix time). It's widely used for server side synchronization
fix(datepicker): typo in test
fix(timepicker): change test to pass in every timezone
fix(tooltip): do not allow show tooltip twice
chore(tooltip,modal): harmonize the isShown variable usage

private $modal.$isShown variable should be the only one used internally while the scope.$isShown variable is only pushed to the scope for end-user usage.
chore(readme): add code climate status
chore(npm): update devDeps
chore(readme): give badges a whole line
chore(readme): add tips back, never say never ;)
chore(release): cut the v2.1.5 release
docs(index): update angular version
docs(app): update angular-strap version
chore(docs): debugInfoEnabled to false
chore(docs): switch to angular-1.3
chore(travis): switch to docker build
chore(docs): revert bootstrap to v3.2 for now