cmake: install libH5mdCore

[junghans]

To prevent:

$ python3
Python 3.6.5 (default, May  2 2018, 16:08:17) 
[GCC 6.4.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import espressomd
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/lib64/python3.6/site-packages/espressomd/__init__.py", line 23, in <module>
    import espressomd._init
ImportError: libH5mdCore.so: cannot open shared object file: No such file or directory
>>> 

[codecov]

Codecov Report

Merging #2277 into python will decrease coverage by <1%.
The diff coverage is n/a.

@@          Coverage Diff           @@
##           python   #2277   +/-   ##
======================================
- Coverage      71%     71%   -1%     
======================================
  Files         377     377           
  Lines       18938   18927   -11     
======================================
- Hits        13577   13564   -13     
- Misses       5361    5363    +2

Impacted Files	Coverage Δ
src/core/energy.cpp	80% <0%> (-3%)	⬇️
src/core/forces.cpp	80% <0%> (-1%)	⬇️
src/core/initialize.cpp	85% <0%> (ø)	⬆️

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