Test Suite for Coding Style test
A new test suite to perform static check on business templates using `CodingStyleTestCase`. This runs a coding style test for each business template, after installing the business template and its dependencies listed in business template metadata. --- In order to start with a test suite with no failure, business templates that does not pass this test today (because they don't install or because pylint issues still needs to be reviewed) are skipped with an ad-hoc `bt/skip_coding_style_test` in the business template. Note that this file is not created by business template system as it is a temporary measure, business templates must pass pylint and other checks from `CodingStyleTestCase`. --- I took the approach of creating one independent test per business template, instead of the approach of creating a site with all business templates like we did in testNamingConventions or testHTML. This appears as another "Coding Style" test, like Performance or Scalability tests. The idea behind this was that if we extend our business template checks ( for example when we translate the [ERP5 Module Creation Guidelines](https://www.erp5.com/documentation/developer/guideline/module) to some scripts we can run on a business template ), we can check that each business template contain what it should contain and not just that the global result is OK. /reviewed-on !629