WICKET-663 enhance ichoicerenderer with id->choice object lookup

Restore IChoiceRenderer as discussed at http://markmail.org/message/nek75o5eftmpkobo
WICKET-5538 When using Component.setDefaultModel, only detach the previous model if the new one is different

(cherry picked from commit 6f791bd8298aab764774938e6b90f7bd1305830d)
WICKET-5531 Create new placeholder tag to indicate where header contributions should appear

Read the header markup ignoring whether the component tag knows its markup class.
I (mgrigorov) don't see the need of this check. No failing tests, no comments why this may be needed...

(cherry picked from commit 1edac84264478a9257a8a4d4f411c0d5a45559ef)
Use Java 7 multicatch
WICKET-5542 Remove final from TextArea.onComponentTagBody()

(cherry picked from commit 32022fdb9e1d2996ac12c7ef3ff13a954ebbbee7)