Nim2 compatibility

[PhilippMDoerner]

closes #182

Makes norm viable with nim devel:

• Swaps ndb for lowdb, which is useable with the current version of nim-devel
• Swaps out generics using [_] to [T] etc. due to breaking change introduced by https://github.com/nim-lang/Nim/pull/21192 See: https://github.com/nim-lang/Nim/issues/21435

Unrelated to that: I introduced nimble tasks to run the tests because I got tired of looking up the exact command after the third time and I'd prefer just having a nimble task for everything related to a package :sweat_smile:

[PhilippMDoerner]

Okay, here we go. @moigagoo I had to significantly revamp the test-suite, solely so we can start testing multiple nim-versions there instead of just one. Couldn't figure out a way that left the calling code within a container itself.

As was visible with the dbTypes issue, it was quite necessary to start testing for multiple versions.

That did sacrifice the docker-compose commands, but I replaced them with (hopefully) as convenient nimble tasks.

Anyway:

• Testsuite runs in github :heavy_check_mark:
• Testsuite runs locally :heavy_check_mark:
• Testuite expanded to run once for 1.6.10 (current stable) and devel (future nim 2.0) :heavy_check_mark:
• Provided new set of commands to easily execute testsuite :heavy_check_mark: