build in container without external dependencies.

[KaiSzuttor]

Fixes #2347
Depends on espressomd/docker#47
Description of changes:

• added a job to gitlab ci
• guarded THOLE in maxset.hpp

[codecov]

Codecov Report

Merging #2406 into python will decrease coverage by <1%.
The diff coverage is n/a.

@@          Coverage Diff           @@
##           python   #2406   +/-   ##
======================================
- Coverage      72%     72%   -1%     
======================================
  Files         397     396    -1     
  Lines       18666   18629   -37     
======================================
- Hits        13496   13454   -42     
- Misses       5170    5175    +5

Impacted Files	Coverage Δ
src/core/communication.cpp	77% <ø> (ø)	⬆️
src/core/forces.cpp	82% <ø> (ø)	⬆️
src/core/energy.cpp	83% <ø> (ø)	⬆️
...core/bonded_interactions/bonded_coulomb_p3m_sr.hpp	0% <0%> (-62%)	⬇️
src/core/forces_inline.hpp	72% <0%> (-2%)	⬇️
src/core/energy_inline.hpp	58% <0%> (-1%)	⬇️
...re/bonded_interactions/bonded_interaction_data.hpp	100% <0%> (ø)	⬆️
src/core/nonbonded_interactions/thole.hpp

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 7a485cc...bbb1b47. Read the comment docs.