+ utils.readfile: support Gamma slc in complex32 format
   - add scomplex to complex32 data type conversion
   - read_binary_file(): support .rslc/rmli file extension
   - read_complex_int16(): refactor to use cpx_band in str for a more flexible output data; revise the output from 2 matrices into 1 matrix
   - read_binary(): support complex32 while calling read_complex_int16(), since it's not supported in numpy.

+ utils.readfile.auto_no_data_value(): add geometrical offset files from alos2App with num of band = 1

+ view.viewer.plot(): set pixels with no data value to np.nan, instead of call np.ma.masked_where(), which seems over-complicated (compared with setting to nan) and I could not recall the reason anymore.

+ cli/prep_isce.py: set -f default from str to list, to be consistent with the non-default var type.

attempt to free up the disk space, and to fix the circle CI testing failure.

This reverts commit 912298e.

to show the full error msg, by reverting part of insarlab#472.