Allow to force the installation of an extension even if dependencies are not satisfied

Actually, this would be a compromise to allow installing extensions and avoiding having to support all extensions on all versions.

Take the following example:
faq application ( https://github.com/xwiki/xwiki-platform/tree/master/xwiki-platform-core/xwiki-platform-faq ) depends on a couple of macros in platform (velocity, box, include, html). This application is released with the platform and versioned the same, and so are the versions of the dependencies.

So, on an xwiki 5.2.1 instance, you will be able to install version 5.2.1 of the faq application but not version 5.2.2 (because of unsatisfied dependencies) although nothing might have changed in the dependent macros from 5.2.1 to 5.2.2, so there is no reason it wouldn't work.

The clean solution would be to declare in the faq application that it would work with other versions as well (but it would be huge work to make the list correct for all extensions).
The dirty solution is the one proposed in this issue, which is to allow extension installers to force install. Of course this needs to not be very very handy in the UI so that if nobody can do it unless they actually understand what it means, but it should be possible. This could also have the advantage of enabling crowdtesting of versions support.