Incremental compilation in j2cl-maven-plugin

[treblereel]

PR: #174

Provided implementation contains the following steps:

1. The feature itself is optional and can be enabled/disabled via the incremental property.
2. At the moment, it requires turbune to be enabled because it uses striped sources produced by turbine to generate .build.map files during the first run and on files changes.
3. The .build.map files are storing the following information:
   • class name - the name of the type
   • hierarchy - if the current type extends another type
   • interfaces - if the type implements interfaces
   • innerTypes - if the type contains inner types
   • deps - list of types extracted from methods parameters
4. The incremental generates .build.map files only for Java classes, so no js or native.js are tracked.
5. On fileChange event, incremental

• copies existing files from the latest successful round
  service.getDiskCache().getLastSuccessfulDirectory to the new location
• compiles the list of changed files and their dependencies from the .build.map files, processes them to j2cl and overrides the existing files, if there are any deleted files, it removes them and their .native.js files if they exist.

6. The .build.map files are updated with the new information and, on successful compilation, the latest location is marked as new SuccessfulDirectory.
7. BuildService is responsible for processing the change set and generating the new ".build.map" files.

• for parsing of stripped sources javaparser is used.