make appbundle target for OSX development

Adds an 'appbundle' target that creates a top-level Bitcoin-Qt.app/
Modifies the 'deploy' target so that it leaves behind Bitcoin-Qt.app;
make clean will remove it.
clientmodel: remove 2 hard-coded values, use CChainParams instead
add SendCoinsEntry::updateLabel() function

- makes the code for updating a label reusable
- no functional changes
Merge pull request #3084 from Diapolo/clientmodel

clientmodel: remove 2 hard-coded values, use CChainParams instead
Merge pull request #3101 from Diapolo/sendcoinsentry

add SendCoinsEntry::updateLabel() function
Merge pull request #3103 from gavinandresen/appbundle

make appbundle target for OSX development