run output improvements

[MasloMaslane]

• Alternative time/memory units in config #26
• replace Time limit (in ms): 1000 with Time limit: 1000 ms, Memory limit (in kb): 16000 with Memory limit: 16000 kB (note also that probably it should be kB instead of kb,
• replace Task Simple test package (abc) with Task: Simple test package (tag: abc),
• list (e.g. in a single line) the tests for which the solutions will be run,
• after printing the list, remind the user about how to regenerate tests and that run runs on the already generated tests,
• give a warning when run runs only on sample test,
• give an error when run runs on 0 tests,

[tonowak]

It's not yet ready for review, correct?

[tonowak]

I've reviewed the current code. We can merge it and implement the last feature in another PR.