Fix compatibility with Python 2.6
Manual initialization is no longer need in umtrx_fft.py.

We have initialization in UHD code nowdays.
Fix copy-paste errors in umtrx_lms.py comments.
Add getters for Tx DC offset calibration to umtrx_lms.py.
Add DC offset slider to the LMS control panel.
Set path to umtrx_lms.py in lms_tune.sh to run it from the default directory.
Minor improvements to umtrx_lms.py.