fix #499, find import self package,import not found package,import repeat package in one file errors

With this pr,the plugin now can find follow type of compile errors:
* import a package which is self (one type of import circle compile error).
* import a package which can not found in current project and sdk.
* import repeat package in one file.

I had split ImportDeclarationInspection into two Inspection classes:
* ImportPathInspection
* ImportUnusedInspection

All test passed.