Small improvements in indentation

Correct indentation for:

* assignments of string and char literals (val x = "abc")
* `else` alignment in brace-less if-else expressions

I needed to improve the testing infrastructure a bit:

* set a document partitioner (the results of indentation
  depend on partitions, and some scenarios worked in the test
  suite, but failed in a real editor)
* correct the new caret position, and allow for tests where
  the expected result has only one occurrence of CARET

Fixed #1001306
Fixed #1000415
Use Scala formatter preferences for TABs in indenter instead of the Java ones.
Merge pull request #657 from dragos/issue/indent-string-assign

Small improvements in indentation