Add support for compiler plugins

[adpi2]

Motivation

Compiler plugins are fully part of the Scala library ecosystem. Some of them like kind-projector are widely used. This should be better reflected in Scaladex, by indexing compiler plugins, and enabling users to search them.

Identified obstacles

Currently, compiler plugins are filtered out by the BinaryVersion.Parser because their binary version is the full Scala version. Example: the binary version of kind-projector_2.13.8 is 2.13.8 instead of 2.13.

We need to accept such binary version and treat it like a ScalaCompilerPlugin platform.

Implementation Guidelines

1. Introduce a ScalaCompilerPlugin subclass of Platform
2. Modify BinaryVersion.Parser to return ScalaCompilerPlugin when the binary version is a Patch version
3. Adapt the front page, search page and project page to include the new compiler plugin platform.

Expectations

1. The indexing of a compiler plugin should be tested
2. The front page, search page and project page should show the compiler plugins
3. The search filters and project page drop-downs should be usable (not too verbose).