Add handling for missing Robot Framework parsing errors

[mnojek]

It's been a long time since we reviewed RF parsing errors and added support for them in Robocop.
We need to see if there are more errors we should support, because RF is being actively developed and new features require additional error handling.

[mnojek]

@bhirsz Do you think we should revisit this issue or maybe it was already done by you along with the recent bugfixes you provided?

[bhirsz]

We still should analyze parsing-errors we're catching - also we may to run robocop -i parsing-error on bigger code base (like robotframework source code). Some of those errors: https://github.com/MarketSquare/robotframework-robocop/blob/master/tests/atest/rules/errors/parsing_error/expected_output.txt may be basis for new rule, or should be included in other already existing rule. I didn't investigate it fully, just covered new parsing-errors added in RF 6.1