rqt_reconfigure: Restore support for parameter groups

I finally got around to restoring group support in `rqt_reconfigure`. From what I can tell, groups were broken by a few commit in January of 2013, and haven't worked right since. Groups currently do not work *at all*, and the only included change outside `param_groups.py` is a trivial one, so I don't expect any serious regressions.

I tried to restore the original intent for the base types (tab, collapse, apply, hidden, box) with box being the default for any unknown types. I haven't added any new group types...yet...

I've done all of my testing using a dynamic reconfigure test project [1] that I created. Feel free to use it to demonstrate the functionality of each type.

I have uncovered two bugs in the python implementation of the `dynamic_reconfigure` client. They present themselves as:
1. Python exception when enabling or disabling a group (primarily visible for the `collapse` type
2. Groups do not maintain order like parameters do

I'll file bugs for these in `dynamic_reconfigure`.

This Fixes https://github.com/ros-visualization/rqt_common_plugins/issues/162
FYI https://github.com/ros-drivers/prosilica_driver/issues/5

Thanks,

--scott

[1] https://github.com/cottsay/dyn_re_test
`items()` copies the data, and `iteritems()` doesn't. I didn't know it broke python 3.3 compatibility, though. I'll change them back to `items()`. Good catch, @dirk-thomas!