Revert "Added index method to InstructionGroup"

This reverts commit cc9af2bb191338f31225c192df9739a28e29f197.

This commit only duplicates the functionality of
InstructionGroup.indexof.
Don't remove debian subdirectory if it exists on git cleanup.

This doesn't harm if you don't build a Debian package as `git cleanup` will work
just fine if the `debian` directory does not exist. Without this patch the
`distclean` rule will also remove the `debian` directory which make it
impossible to correctly build a debian package.
Merge pull request #1916 from venthur/fix/dont-remove-debian-subdir

Don't remove debian subdirectory if it exists on git cleanup.
Merge pull request #1888 from inclement/master

Revert "Added index method to InstructionGroup"

I agree index is a better name, and a better implementation is probably worthwhile, but I think a method rename may as well wait until version 2 with the other breaking changes that have accrued. I guess improving the existing method can go in a different pr, I will merge this one for now.
Document fixes to label padding.
Document that widgets created before load_file was called doesn't have styling.
doc line_height vs minimum_height of TextInput.