The merge type is a per repository setting. Add it to the edit page.

Add the option to merge a ticket branch to the integration branch
only when it can be fast-forwarded, or
always with a merge commit, or
by fast-foward if possible, otherwise with a merge commit.

Adds a new property ticket.mergeType with the valid values
FAST_FOWARD_ONLY, MERGE_ALWAYS and MERGE_IF_NECESSARY.

Merging and canMerge were refactored to make use of a new
IntegrationStrategy class for each type of strategy.

If the source repository access restriction exceeds the fork default (push)
then the fork shall inherit the source repository access restriction.

Also switch back to Maven Central repository.