Add warning message for Submit build

When submitting builds, sometimes the current user logged in is not the same
as the one assigned to this package.

This change will show a warning if someone tries to build a package which he/she
does not own.

It will suggest the user to use the 'Assign To Me' button to assign that package
to him/her.
Merge pull request #121 from thescouser89/prod

Add warning message for Submit build