qtgui: timing is handled in the blocks; removing the qt timer.

This update dramatically reduces the X server overhead of the QT sinks.
Merge branch 'maint'
qtgui: adds ability to set the graphics style rendering of the qtgui sinks.

Set through gr-qtgui.conf prefs file. Documented in QT GUI section of manual.
qtgui: fixed call to _a version of volk kernels for waterfall plots.

(same fix tha was applied to freq_sinks in bf6d843ebde3a36).
Merge branch 'maint'

Conflicts:
	gr-qtgui/lib/waterfall_sink_c_impl.cc
	gr-qtgui/lib/waterfall_sink_f_impl.cc

Conflict due to white space issues.
grc: fix error message in console when using qtgui blocks
build: moving the location of the config.h file in the build tree so we can access it in sources as gnuradio/config.h.

Also uses the config.h to pull out if we've defined GR_PERFORMANCE_COUNTERS to handle the setup_pc_rpc function if perf counters are/are not compiled in.
cmake: Adds GR_CTRLPORT as a define in the root directory to populate config.h properly.
Merge branch 'maint'
blocks: allow subtract block to take a single input to invert the sign.
blocks: allows null source/sink to output/input multiple streams.

Updats xml files to allow this and to set bus port connection vector to group ports.
filter: adds a ccf version of the fft filter.

Taps are converted to complex still, so no computational savings here. Just for convinience of setting taps (mostly in c++).
filter: use fft_filter inside pfb_decimator.

Depending on the decimation rate and filter size, filtering with time domain or freq domain can be slower/faster and rotating using expj or fft can be slower/faster. This enables users to decide which features to use.
filters: fixing up some minor issues with the analysis/synthesis filterbanks.

Also adds bus ports capabilities to these filterbanks. Using the GRP properties box, the vector for the bus ports can be set up to group and redirect each channel as necessary.
Merge branch 'pfb_reconstruction'

Conflicts:
	gr-filter/python/filter/pfb.py
filter: compare as integers to make sure we're within the right bounds.

Fixes CID 1189413: Unsigned compared against 0 (NO_EFFECT)
filter: set fft and ifft pointers to NULL not 0 in constructor.

Addresses CID 1189412: Explicit null dereferenced (FORWARD_NULL)
Merge branch 'maint'
filter: completing previous fix for CID 1189412 for new ccf filter on master.
runtime: setting proper default value for log_level if no prefs file is found.