obspy-scan: plot and print overlaps

[megies]

This adds plotting (blue bars, like the red bars for gaps) and also printing (with option "--print-gaps") of overlaps.

• slight change in handling of endtimes: use endtime+delta for end of time segments -> cleaner handling of gaps/overlaps
• fix compress_start_end helper function: overlaps were actually always merged, even with merge_overlaps=False
• increase coverage by testing stdout for option --print-gaps
• save obspy version in obspy-scan npz output

[codecov-io]

Current coverage is 86.28%

Merging #1366 into master will decrease coverage by -0.01% as of de188a3

@@            master   #1366   diff @@
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  Files          369     369       
  Stmts        50102   50127    +25
  Branches         0       0       
  Methods          0       0       
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+ Hit          43234   43250    +16
  Partial          0       0       
- Missed        6868    6877     +9

Review entire Coverage Diff as of de188a3

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[megies]

Rebased. No objections so far, gonna merge this when CI passes.

[krischer]

I'll do it. I was gonna object to the ugly colors ;-) But matplotlib 2.0 will change all styles in any case so we can revamp our plots when its released.

[megies]

I was gonna object to the ugly colors ;-)

Only color I added is ordinary blue.. ;-) But yeah.. getting rid of these old mpl colors will be good to see.