Allow more convenient database initialization

[vitusortner]

This PR also introduces the functionality for customizing the name of the database file.

Resolves #100.

[codecov]

Codecov Report

Merging #116 into develop will increase coverage by 1.44%.
The diff coverage is 100%.

@@             Coverage Diff             @@
##           develop     #116      +/-   ##
===========================================
+ Coverage    68.69%   70.13%   +1.44%     
===========================================
  Files           46       48       +2     
  Lines         1265     1326      +61     
===========================================
+ Hits           869      930      +61     
  Misses         396      396

Impacted Files	Coverage Δ
floor_generator/lib/writer/database_writer.dart	75% <100%> (+0.45%)	⬆️
floor_generator/lib/writer/floor_writer.dart	100% <100%> (ø)
..._generator/lib/writer/database_builder_writer.dart	100% <100%> (ø)

---

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 78136f4...9bb5642. Read the comment docs.