Capture all keys and store active modifiers
Allow multiple token selection only with ctrl and left click

A normal left click without ctrl deselects any previous multi-selection.
Add spec for key capture directive
Add spec for key capture service
Fix tree spec.
Add test for head change to e2e tree spec
First minimal change head implementation
Exit grunt process with error if protractor test fails
Fix typo
Enable multiple head change
Start to add specs for head changing
Circumvent mutation by specs

The tokens are changed by the tests and so a beforeEach setup
would not be possible without moving the creation into a function.
Add headsFor function to state service
Handle change head of an inner node to a leaf
Remove duplicated code
Add first spec for multiselection head change
Unify spec setup
Add selection specs
Merge pull request #99 from latin-language-toolkit/change-head

Change head