CPU-load-dependent Decimation:
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* To get a smooth output when using UHD as source, a CPU-dependent decimation has been implemented. The parameter self.decimation_step sets the step-size to increase/decrease the decimation-factor --> Use with care - see known problems!
* Decimation is increased as long as AT LEAST ONE of your system's CPUs stays less than 10 % in idle mode (more than 90 % load).
* Decimation is decreased as long as EVERY of your system's CPUs stays more than 70 % in idle mode (less than 30 % load).
* In the class "_cpu_usage_watcher_thread" you can set the interval (also update-interval) for the CPU-load to be measured (self.measurement_interval)

Known Problems:
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* bad_alloc errors are possible if decimation or block_len is getting to high (limited buffer-size in GNU Radio -> problem with building vectors needed for decimation)
  ---> In most cases, the decimation could be set much higher (refresh-rate of 50-100 Hz adequate for the plot -> actual refresh-rate much higher (sample_rate / block_len)!)

Howto add your own blocks to the GNU Radio Spectral Estimation Toolbox - GUI:
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
* Add new blocks to the specest_window.ui (Use Qt4-Designer -> simply add a new tab with scrollarea, select useful field-names etc.)
* Run "pyuic4 specest_window.ui -o specest_window.py"
* Open specest_window.py and add the following lines at the beginning of the file:
	from PyQt4.Qwt5 import QwtPlot, QwtCounter
	import PyQt4.Qt as Qt
  Delete the last two lines of the file.
* Now add a new class at the beginning of specest_gui.py
