Improve logging and user-facing output

[fghaas]

A few changes primarily concerned with making olx new-run a bit more user-friendly in its output:

• Add some debug logging to ArchiveHelper (recording what files are being added to the archive)
• Add some debug logging to GitHelper (recording what git commands are being run)
• Suppress unhelpful git messages from user-facing output
• Stop telling people that they should switch back to master, when their run branch is not based on master

[codecov-io]

Codecov Report

Merging #40 into master will decrease coverage by 0.08%. The diff coverage is 94.73%.

@@            Coverage Diff             @@
##           master      #40      +/-   ##
==========================================
- Coverage    97.9%   97.81%   -0.09%     
==========================================
  Files          15       15              
  Lines         858      870      +12     
==========================================
+ Hits          840      851      +11     
- Misses         18       19       +1

Impacted Files	Coverage Δ
tests/test_git.py	100% <ø> (ø)	:arrow_up:
olxutils/cli.py	94.52% <ø> (-0.04%)	:arrow_down:
olxutils/git.py	100% <100%> (ø)	:arrow_up:
olxutils/archive.py	97.14% <85.71%> (-2.86%)	:arrow_down:

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