New Dwarf2 plugin that supports x64 binary

[HighW4y2H3ll]

The idea of this patch is to add x64 support for taint analysis of DWARF symbols. The pri_dwarf plugin is rewritten into dwarf2 plugin to support the extension of new architectures. Now the pri_dwarf plugin is split into two parts: the first part is a Python script that reformats the outputs of dwarfdump command into a few JSON files, and the second part is the dwarf2 plugin which takes in the pre-processed DWARF info.

In conclusion, this patch includes:

• A Python script that dumps Dwarf info into JSON files. (dwarfdump.py)
• dwarf2 PANDA plugin that replaces the old pri_dwarf plugin.
• Fixups in pri_taint PANDA plugin to use new dwarf2 plugin.
• Other minor fixes in file_taint and stringsearch plugins

[lacraig2]

This PR isn't passing tests for reasons unrelated to it.

It does pass test_installer which indicates that it all compiles.

I will be merging this without tests if no one objects within a day or so.