Require assets with logical paths, where possible

The latest versions of Sprockets parse `bower.json` and set-up the
logical path to be translated to the source file specified in the
'main' property.

N.B.
- the path for the main file of older versions of angular-ui-date is
  incorrect.
  See 346e1e0126.
- this is not yet working with Caret.js.
- 2.2.2.backport2 had broken support for Bower projects.
  See 960e2f5.

Signed-off-by: Alex Coles <alex@alexbcoles.com>

app/assets/javascripts/application.js.erb

@@ -38,12 +38,12 @@
 // WARNING: THE FIRST BLANK LINE MARKS THE END OF WHAT'S TO BE PROCESSED, ANY BLANK LINE SHOULD
 // GO AFTER THE REQUIRES BELOW.
 //
-//= require jquery/jquery
-//= require jquery-ujs/src/rails
-//= require jquery-ui/ui/jquery-ui
+//= require jquery
+//= require jquery-ujs
+//= require jquery-ui
 //= require jquery-ui/ui/i18n/jquery-ui-i18n
 
-//= require jquery.atwho/dist/js/jquery.atwho
+//= require jquery.atwho
 //= require Caret.js/src/jquery.caret
 //= require jquery_noconflict
 //= require prototype
@@ -56,7 +56,7 @@
 //= require lib/jquery.colorcontrast
 //= require lib/jquery.trap
 
-//= require select2/select2
+//= require select2
 
 //= require top_menu
 //= require action_menu
@@ -76,9 +76,9 @@
 //= require versions
 //= require_tree ./specific
 
-//= require angular/angular
-//= require angular-animate/angular-animate
-//= require angular-ui-select2/src/select2
+//= require angular
+//= require angular-animate
+//= require angular-ui-select2
 //= require angular-ui-date/src/date
 
 //= require openproject-ui_components/app/assets/javascripts/angular/ui-components-app