Also add the conflict-marker plugin. This should also be useful
for doing rebases and resolving conflicts. Might drop one later
if one of them serves all the purposes in all cases.
While at it, add unimpaired style bindings for moving between
tabs. This is required since :DiffConflictsShowHistory opens
a new tab and default tab navigation bindings gt/gT at least
are binded to something else in python.
Signed-off-by: Sanchayan Maity <maitysanchayan@gmail.com>