libtracker-extract: Remove from examples/ this library is now private
build: Large update to configure.ac including new --enable-minimal option

Updates include:

1. Now you can use --enable-minimal, and only tracker-store is built and
   command line utilities, everything else is disabled.
2. All ./configure arguments have been updated to use $enableval and $withval.
   This fixes cases where the --disable-* variant is used. This has also fixed
   some cases where the AC_ARG_ENABLE or AC_ARG_WITH 'if-not-given' was used
   incorrectly.
3. There is now a --enable-tracker-extract (default is enabled), now it can be
   disabled.
4. There is now a --enable-tracker-writeback (default is enabled), now it can
   be disabled.
5. Summary now reflects what is built more concisely and is much smaller when
   using --enable-minimal.
6. After running autoscan, ./configure now has more checks for PROGS, HEADERS
   and FUNCS that are being used.
7. AC_USE_SYSTEM_EXTENSIONS is now used adding C extensions where available
   (like _GNU_SOURCE).