Capability to read input from classpath resource instead of filesystem

[levsa]

These changes adds support for reading input from resources in classpath instead of file system, using:
input="classpath:/path/to/resource".

Drawbacks:

• Support for changing files in place is disabled, since input streams are used instead of files.
• Possibly the behaviour of duplicate inputs in PropertiesActionProcessor is changed (files are not resolved first anymour, only input strings are compared).

[levsa]

If it is necessary to keep the possibility to use the input file as output, I could look into supporting that as well.