feat(datepicker, timepicker, select): CSS icons customization

Add possibility to customize CSS classes for top/bottom/left/right arrow icons used in datepicker and timepicker and checkmark icon used in select
feat(dropdown): add 'target' attribute to links generated in dropdowns

There are cases when one needs to explicitly specify anchor 'target' attribute, for example to bypass angular router and make actual server request
fix(dimensions): use boxRect for width an height
Merge branch 'master' of https://github.com/mgcrea/angular-strap into prod

Conflicts:
	src/timepicker/timepicker.js
	src/timepicker/timepicker.tpl.html
fix(timepicker): merge typo