Allow host:port specification for memcached storage backend

[hummeltech]

So that MemcacheD hosts and ports other than localhost and 11211 can be used.

Also:

• Added ctest --parallel execution support
• Added tests for custom MemcacheD {host}:{port}
• Added tests for AddTileConfig/AddTileMimeConfig

[codecov-commenter]

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Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 65.53%. Comparing base (a346728) to head (507b942).
⚠️ Report is 87 commits behind head on master.
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Additional details and impacted files

@@            Coverage Diff             @@
##           master     #369      +/-   ##
==========================================
+ Coverage   64.81%   65.53%   +0.72%     
==========================================
  Files          23       23              
  Lines        4604     4611       +7     
==========================================
+ Hits         2984     3022      +38     
+ Misses       1620     1589      -31     

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