corrected wrong message
redesigned priority. refs #9.

Now priority of all bugInstance (and rules for sonar) is redesigned.

HIGH:   SLF4J_PLACE_HOLDER_MISMATCH, SLF4J_FORMAT_SHOULD_BE_CONST,
        SLF4J_UNKNOWN_ARRAY and SLF4J_ILLEGAL_PASSED_CLASS are
        high priority. They might make product wrong.

NORMAL: SLF4J_LOGGER_SHOULD_BE_PRIVATE, SLF4J_LOGGER_SHOULD_BE_FINAL
        and SLF4J_SIGN_ONLY_FORMAT are normal priority. They make
        code and log difficult to read.

LOW:    SLF4J_LOGGER_SHOULD_BE_NON_STATIC is low priority. This bug
        only points about coding policy.
changed bug categories
findbugs report should contain INFO level warning.
Merge pull request #11 from eller86/redesign-priority

Redesign priority and category