Support preserving case when replacing.

When making a case insensitive search, try to keep the string capitalization when doing
the replace:
      - All upper-case matches are replaced with the upper-case new	text.
      - All lower-case matches are replaced with the lower-case new text.
      - Capitalized matches are replace with the capitalized new text.
      - Other matches are replaced with the new text as provided.

Note: this does not work with regexp replace, only plain text.

Change-Id: I87cbc28eb64688bdf3c8c6ec173fcb22f91abcd0
Reviewed-by: Cristian Tibirna <tibirna@kde.org>
Reviewed-by: Leena Miettinen <riitta-leena.miettinen@digia.com>
Reviewed-by: Eike Ziller <eike.ziller@digia.com>