We put them below all other imports, checkstyle defaults to below
each group.

Also fix the formatting of the checkstyle config, replacing tabs
with spaces and fixing broken indentation/spacing.

Change-Id: I46f71e58f9ff4f8719ba59ff95d6415095058d21
Reviewed-on: http://gerrit.dmdirc.com/3121
Automatic-Compile: DMDirc Build Manager
Reviewed-by: Greg Holmes <greg@dmdirc.com>

This was previously all under checkstyle/ which is weird as there's
a whole bunch of non-checkstyle stuff. Move everything into the nice
etc/ folder to keep it out of the way and sanely organised.

Change-Id: I0df52e8eddc6588c775a5173b624144807f1e59a
Reviewed-on: http://gerrit.dmdirc.com/3102
Automatic-Compile: DMDirc Build Manager
Reviewed-by: Greg Holmes <greg@dmdirc.com>