Updated CMake to add 'make install' and 'make uninstall'

[jmcorgan]

• Installs libzercoin.so to $PREFIX/lib
• Installs Zerocoin headers to $PREFIX/include/zerocoin
• Installs bignum headers to $PREFIX/include/zerocoin/bitcoin_bignum
• Installs pkg-config file for library name 'zerocoin'

[jmcorgan]

This is the same as #6, but properly configured the pull request to go into dev branch.