Add icons to switch between side-by-side and unified diff view

For change edits the icon is not displayed, because the unified diff
view is not able to handle change edits yet.

Change-Id: I02b9800d40a510b9f90d6890e619aec89c8933d5
Signed-off-by: Edwin Kempin <edwin.kempin@sap.com>
Add support for diff web links

Plugins can now add web links to the diff screen that will be
displayed next to the navigation icons.

Change-Id: Ifa01103054c3e81e3121c219ee5b69db2fefb3bf
Signed-off-by: Edwin Kempin <edwin.kempin@sap.com>
Merge "Add icons to switch between side-by-side and unified diff view"
Merge "Add support for diff web links"