WIP New classpath and sourcepath implementation

This is WIP branch pushed to consult it with Grzegorz Kossakowski.
 
Current implementation of classpath is not very efficient and it's quite abstract because it was created when e.g. .NET was supported. Therefore one of goals of new implementation is to improve efficiency by creation of dedicated classes for various file types characteristic for Scala with JVM backend - what allows us to create more efficient, more low-level operations. The second goal is to reduce memory consumption. To do that there's added caching for jar/zip files. So that we can reuse existing instances, when we create entries for the same files once again. Hopefully it will lead to significant reduction of used memory also in the case of e.g. ScalaPresentationCompilers.
 
One of the most important things took into account during creating this implementation was adding it as optional feature, which can be marked as experimental and turned on  using flag. At the beginning users will use old classpath implementation by default and they will be able to use new implementation when:
- they will want to test it (feedback)
- they will want to gain benefits which it provides
 
There are a lot of TODOs, some unused classes, temporary (?) benchmarks and maybe not very pretty solutions and names, but it's something, what will be discussed with Grzegorz. Definitely we need more unit tests. Right now existing tests (including partest) and also other, manually executed tests pass.
 
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