Pylint checks round 2. Some code cleanup.

### Motivation
Activate a bunch of `pylint` flags that are somewhat important for clean (if not correct) code. Drop some dead code.

### Changelog
* Enable colorized `pylint` output.
* Activate the following pylint flags: `E0202`, `E0611`, `W0221`, `W0232`, `W0621`, `W1201`, `C0301`, `R0901`. See the [documentation](http://docs.pylint.org/features.html) and the commit messages.
* Fix most of the errors detected; suppress the rest.
* Remove some redundant test files.