QtGUI updates: new time sink block

I have added a new qtgui_time_sink block (for complex and float) to GNU Radio in the git master repo. This block just displays the time-domain waveform of a set of signals. Most importantly, I think, is that it allows us to connect multiple signals to the sink that will be plotted on the same time axis.

Each signal has a name and dfferent color that is specified in the plot legend. The signals can also have their name changed with set_title(which, name) where which is the index of the signal to be be renamed to name. It also has a set_color(which, color) to set the color of the signals, where color is a string name for a color, which are those available in Qt and can be found in the QColor documentation under "Predefined Colors." These settings can also be adjusted through the Qt signal/slot concept by emiting the signal with the proper values. A pyqt_time_c.py and pyqt_time_f.py examples in the gr-qtgui/apps show both of these concepts and how to attach multiple signals.

This is the first in a series of updates I plan on making to our gr-qtgui interface. I should be able to split out the other components into individual blocks, like the FFT, waterfall, and constellation plotting tools. I should also hopefully be able to improve the efficiency of the system and add more capabilities to these plotters.