config: move various py templates to kallithea/templates/py/

For some reason, we had some python templates in kallithea/config .
kallithea.config is mainly the TG entry point, and thus a high level controller
thing - not a place to store templates.

Instead, use the templates directory and introduce a new py subdirectory.

With git hook templates in a templates directory, there is no need for tmpl in
the name.

.coveragerc: fix reporting of coverage to match what is run

Without this change, the HTML report will show all lines specified in
run.omit. As they have 0% coverage, this will negatively impact the overall
coverage percentage calculated in the report.

Note: at this moment, we have an overall 74% test coverage.
Test by installing pytest-cov and running:
py.test --cov=kallithea --cov-config=.coveragerc --cov-report html
and opening htmlcov/index.html in a browser.

.coveragerc: remove reference to non-existing paster_commands dir

The corresponding code is now in kallithea/bin/, which is already in the
omit list.

tests: add pytest-cov .coveragerc file

When using pytest-cov this file can be used to configure the coverage report.
See https://coverage.readthedocs.io/en/latest/config.html for details.
So when you start py.test like this

py.test --cov-config .coveragerc --cov=kallithea --cov-report xml

the settings in this file will be used.