NavCollapse has fixed height on first collapse

- Fixed typo for "nav-collapse" (was "nav_collapse")
NavCollapse has fixed height on first collapse

- NavCollapse now uses the "nav_collapse collapse" class instead of
"nav_collapse" to fix the issue with a fixed height when collapsing the
first time.
- Removed data_target from Boostrap as it's already in Constants.

NavCollapse has fixed height on first collapse

- Fixed typo for "nav-collapse" (was "nav_collapse")
Merge remote-tracking branch 'upstream/master' into NavbarCollapseFixedHeight
Merge branch 'NavbarCollapseFixedHeight' of https://github.com/acramatte/gwt-bootstrap into NavbarCollapseFixedHeight
Merge pull request #457 from acramatte/NavbarCollapseFixedHeight

Navbar collapse fixed height