Sb/file types handling

[basaks]

1. Conv2tif outputs files with the following file extensions.

   
   IFG = '_ifg'
   COH = '_coh'
   DEM = '_dem'

2. Added new metadata type for the coherence files - both conv2tif output and prepifg output.
New metadata

conv2tif output: ORIGINAL_COH

Prepifg output: MULTILOOKED_COH

3. Manual refx/y error fixed
4. A lot of unused config.py functions removed, corresponding tests removed. Required functions updated.

[codecov-commenter]

Codecov Report

Merging #270 into develop will increase coverage by 2.05%. The diff coverage is 100.00%.

@@             Coverage Diff             @@
##           develop     #270      +/-   ##
===========================================
+ Coverage    90.72%   92.78%   +2.05%     
===========================================
  Files           25       25              
  Lines         3386     3089     -297     
  Branches       567      494      -73     
===========================================
- Hits          3072     2866     -206     
+ Misses         206      138      -68     
+ Partials       108       85      -23     

Impacted Files	Coverage Δ
pyrate/core/orbital.py	95.70% <ø> (ø)
pyrate/core/prepifg_helper.py	95.13% <ø> (ø)
pyrate/default_parameters.py	100.00% <ø> (ø)
pyrate/configuration.py	100.00% <100.00%> (ø)
pyrate/conv2tif.py	100.00% <100.00%> (ø)
pyrate/core/config.py	93.44% <100.00%> (+12.82%)	:arrow_up:
pyrate/core/gdal_python.py	85.14% <100.00%> (+0.17%)	:arrow_up:
pyrate/core/ifgconstants.py	100.00% <100.00%> (ø)
pyrate/core/ref_phs_est.py	95.60% <100.00%> (ø)
pyrate/core/roipac.py	91.52% <100.00%> (ø)
... and 7 more

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[mcgarth]

Approved