Implement Method#getDefaultValue()

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Make sure that Proxy instances of annotations inherit the default values

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Use the default value in annotations' proxies

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>