Change (%CATEGORIES%) to %GROUPS% in PKGBUILD.in files.

The parenthesis were present in both the info files and the PKGBUILD.in
files. I also figured I would make the field naming more consistent
while I was fixing the parenthesis.
Add a gitignore file to the packages directory.

We have to ignore the generated aur/ and repo/ directories.
Remove the '-svn' and '-git' suffixes from packages.

The package directory name is used as the package name when generating
repo packages. We want clean names for those.