IDEA-83595 Allow adding more than one gradle project

Re-written import and settings management infrastructure in order to allow a single ide project to be backed by multiple external projects
IDEA-83595 Allow adding more than one gradle project

1. Clarified ProjectDataService.importData() contract;
2. Corrected ModuleDataService and LibraryDataService accordingly;
IDEA-83595 Allow adding more than one gradle project

Compilation fix (ide 'make' bug that it didn't show it earlier?)
gradle 1.6-rc-1 is applied