Plugins: Fix bug in stopping a ClientApp plugin with $parameters in the args
Data: Clear more caches when under memory pressure and at shutdown
build.xml: signing

- move signing to ant macros so they can be used by multiple build targets
- add support for signed devbuilds
- add support for generating i2pseeds.su3 (for testing)
merge of '1e0d390eeacce432f968251f1bbbe03ef031a116'
     and 'f61d617d9bfd5759366102b0b5ff45effde08e84'