rqt_reconfigure: Re-write widget data flow

rqt_reconfigure is virtually unusable as is, and sends duplicate and unnecessary updates to the server frequently. This patch updates the PyQt widgets' structure to address many of the issues reported with rqt_reconfigure.
Merge pull request #209 from cottsay/rqt_reconfigure-editor-rewrite

rqt_reconfigure: Re-write widget data flow
disable info message when selecting nodes
rqt_reconfigure: Update maintainer
rqt_reconfigure: Cache received param changes

rqt_reconfigure: Unify update value naming

Currently, the 'old value' is cached when we send changes (so we don't send an unnecessary update). When the value is changed externally, however, we should update the 'old value' to prevent unnecessary updates here, too.
rqt_reconfigure: Clean up console messages
rqt_reconfigure: Improve checkbox behavior
rqt_reconfigure: Use signals to trigger GUI updates
Merge pull request #210 from cottsay/groovy-devel

rqt_reconfigure: Editor widget re-write, Round II
list image transport topics if parent image topic is not available (fix #215)
rqt_reconfigure: Use a single dynamic reconfigure client
Merge pull request #213 from cottsay/groovy-devel

rqt_reconfigure: Use a single dynamic reconfigure client
using CATKIN_ENABLE_TESTING to optionally configure tests
rqt_plot: redraw plot only on new data to reduce cpu load, especially with matplot (fixes #219)
Merge pull request #220 from scpeters/catkin_enable_testing

Use CATKIN_ENABLE_TESTING to optionally configure tests
rqt_bag_plugins: fix PIL/Pillow error.

Fix #224
Merge pull request #225 from bchretien/groovy-devel

rqt_bag_plugins: fix PIL/Pillow error.
rqt_plot: don't add more padding for each additional curve
rqt_plot: don't have required minimum padding

With a fixed absolute minimum padding, rqt_plot is useless for plotting
arbitrarily small values. (For example, trying to plot a magnetic field
measured in teslas, usually having a magnitude of about 1e-4.)
Merge pull request #223 from forrestv/zero_abs_padding

rqt_plot: decreased required minimum padding to 0