This commit adds support for the frege intellij plugin by

 - exposing the frege compiler jar as a dependency, so the plugin can
   recognize the standard library.
 - adding the name 'fregeRun' as that is used by the plugin to run files
 - add support for overriding the main module executed by runFrege so
   that arbitary files can be run by the plugin

The following applies if the frege compiler is run with the `-make`
[flag](https://github.com/Frege/frege/wiki/Compiler-Manpage#make-mode):
Given two dependent frege files. If the `mainSourceDir` property is not
correctly configured, then the frege compiler cannot find the dependent
frege file and will therefore fail the compilation.

The frege compiler starts at the `mainSourceDir` and searches
recursively for dependent modules. E.g. If `mod.Main.fr` imports `other.Dep.fr`
then the frege compilers searches for `mainSourceDir/other/Dep.fr`.

The name implementation is already used by the java plugin and it
leads to conflicts when combining both plugins.

This adds the following common tasks:
- clean
- check
- assemble
- build
- buildConfiguration task rule
- clean task rule

its dependencies

The replFregeTask has the following new logic:
1. Compiles the specified fregeRepl module (either in the
   `build.gradle` via command line option `--replModule=...`) and all
   its dependencies.
2. Sets up the correct classpath so that dependent modules don't have
to be imported manually. In addition, it solves the shadowing problem by
removing the replModule java and class file from the classpath.
3. It prints one single command to directly start the repl and load the
   specified module.

Bonus: I designed the task so that you can even automate step 3 with
the following bash command: `eval $(./gradlew -q replFrege)`.