Remember last sign-off setting, indicate setting status near Commit button

The 'Sign off' commit option (--signoff) should be remembered (either on a global or a on a per-repository basis). Currently the option is forgotten on a restart of SourceTree.

Also, it will be good to have indicators near Commit button to indicate the status of the chosen 'Commit options'. I'm especially interested in knowing with one look whether the 'Sign off' option is enabled or disabled. But it will also be nice to have indicators for options like 'Amend last commit'. Currently I have to remember to pull down the 'Commit options' drop-down menu to see what options are enabled or disabled.