LintIgnore: field for ignoring lint errors

Every linter provides a method to ignore some of the checks. This provides a way to globally ignore a specific fdroid lint error by adding the error text to a list field called LintIgnore:. See the text case for an example. This is a global disable. The metadata parsing does not currently provide access to the comments, so it would not be easy to create a per-line disable, like # pylint: disable=... or # yamllint disable. I'll leave that to future work.