Fix RepositorySearchDialog when browsing different directories

When clicking "Browse" multiple times for different directories
containing repositories the RepositorySearchDialog only displayed the
repositories selected in the last browse step but also added
repositories selected in earlier browse steps. This is surprising as the
latter weren't displayed before finishing the wizard.

Bug: 450213
Change-Id: I6081f933000b6f92c73ac7817d625b0472ca1f2f
Signed-off-by: Matthias Sohn <matthias.sohn@sap.com>
Extract hover manager of CommitGraphTable into own file

This is a refactoring because the class will have to grow in the next
change.

Change-Id: I04022b27c8beddaa34acdeceb2982c70f8344f1f
Signed-off-by: Robin Stocker <robin@nibor.org>
Signed-off-by: Matthias Sohn <matthias.sohn@sap.com>