glib/gst-plugins-bad: Don't pull in dtls/datagram patches

We don't actually use those patches, and the code will likely change a lot
before it gets merged upstream.

See discussion on: https://bugzilla.gnome.org/show_bug.cgi?id=697907
gettext: Fix build on OSX

The preprocessor can't find headers if we don't pass -isysroot to it too.
Always include the sysroot in CC/CXX/OBJC/CPP already for iOS/OSX

Otherwise they might not find headers like stdio.h and others.
Add notes about it being a submodule.
Update README.md
build-gst-plugins-bad: Removed ext/dtls make && make install
Added subversion and git as dependencies
javascriptcore: On Linux base64 has no -D and -o parameters

Fixes issue #7
openh264: Use standard include path

Otherwise we're incompatible with the openh264 versions installed
manually from the upstream build system.
Fix openwebrtc-gst-plugins build
build fails on stock kubuntu 64-bit without the gperf package
libusrsctp: Fix build on iOS by using the correct path for the headers that are copied

Use the same method for identifying the iPhoneSimulator SDK as we have
used elsewhere
Fix openwebrtc-gst-plugins-build after OpenSSL autoconf check

Added OPENSSL_CFLAGS to CFLAGS and OPENSSL_LIBS to LIBS