Made LibDRAMPower independent from xerces.

I've shuffled around some code to actually create a library that has no references to xerces anymore. The problem with the old way of doing things is that all objects were included into the .a file, which also included the xerces headers and associated dependencies. This is my attempt at separating things. There are now 2 libraries, 1 that has the core of the model, and one that has our wrappers for xerces.

You can link against the first library without requiring xerces.
To test:
```bash
make clean
make lib
make parserlib
cd testing_library
make clean
make
./library_test
make clean
USE_XERCES=0 make
./library_test
```
Note that the second run of library_test segfaults "by design" since it tries to use an uninitialized memspec object as input. But the important point is that it compiles and links properly.