grc: design time values for object-like variables
digital: using new var_value for constellation variables
grc: allow blocks to dynamically hide some of their ports
uhd: Updated docs, in particular for the command interface
uhd: Added command interface to uhd source, modified command syntax
uhd: Refactored common stuff from usrp sink and source
uhd: Added GRC bindings for command interface
uhd: Added more type checking and flexibility to commands and tags
uhd: Added example for re-tuning through messages
uhd: Added checks for lock sensors.

When operating with an external ref, in MIMO mode or with a GPSDO,
the constructor now waits until the lock sensors report succesful
locking.
If this fails, a warning is displayed using the logger interface,
to keep backward compatibility.
runtime: fix a circular dependency for older compilers
build: missed gnuradio-uhd in static libs build.
Merge remote-tracking branch 'gnuradio-wg-grc/grc_variable_blocks'
Merge remote-tracking branch 'gnuradio-wg-grc/grc_hide_ports'

Conflicts:
	grc/base/Port.py
	grc/gui/Block.py
grc: fixing xml files of some blocks with message control ports to be able to hide/show them as wanted.
grc: fixing some spacing issues in various xml files.
qtgui: adding ability to set grid on/off from grc properties dialog boxes for all qtgui sinks except the "sink" which doesn't support this.

Addresses issue #688. Keeping default to off since the grid's not the prettiest thing.
qtgui: allows users to set title and unit of Y axis for qt time plotter.
Merge branch 'maint'
grc: auto-hide port labels