Improve usage text, error and warning output in batch compiler

Improve usage text, error and warning output in batch compiler

- Usage texts are now printed to stdOut, no longer stdErr.
- 'java ...Main -?' no longer prints usage text twice (once to stdOut
  and then again to stdErr).
- AjdtCommand.inferKind: Usage texts are no longer mis-identified as
  warnings or errors just because they contain substrings "warning" or
  "error". Matching is now more precise, looking for "[warning]" and
  "[error]". But in that case the method would not be called anyway
  because errors and warnings are identified in other ways already. As a
  fall-back, the categories IMessage.ERROR and IMessage.WARNING still
  exist in the method.
- In case of compile errors, no usage message is printed anymore,
  because previously the user had to scroll up a lot in order to see the
  actual messages. This is also in line with ECJ. The same is true for
  warnings, but it was like this in Ajc already.
- AjdtCommand.inferKind: There is a new category IMessage.USAGE
  especially for AspectJ usage texts, which will be identified by string
  matching and then correctly handled (i.e. printed to stdOut, not
  stdErr).
- Usage text printing is no longer done in AspectJ but in the AspectJ
  "shadows" fork of JDT. This helps to get rid of some now obsolete code
  here.

Signed-off-by: Alexander Kriegisch <Alexander@Kriegisch.name>