Update to PJSIP 2.2

This patch introduces a number of changes for the upgrade to 2.2:
 * Removed patches, since they're in 2.2
 * Added option to build from HEAD
 * Enabled the building of shared libraries
   * Can be disabled with --disable-shared
 * Build using external libraries instead of bundled libs
   * Can be disabled with --use-bundled-libs
 * Properly build against homebrew's OpenSSL install