Add FindPatch.cmake

FindPatch.cmake is used on Windows (MSVC) platforms to find patch.exe.
It currently only looks in msysgit/bin (and system paths) but this can
be easily extended.

PATCH_SCRIPT_PATH is now used to specify the location of patch.sh/bat.
As such SCRIPT_PREFIX has been removed.

Rationale for change:
* Modifying your path may require admin permissions for MSVC
* CMake now exits with an error message on MSVC if patch.exe cannot be
found
* Fewer manual steps when setting up Desurium on MSVC
Remove reference to TortoiseGit

TortoiseGit does not include patch.exe as indicated (msysGit does
however) and as such is superfluous.
Correct reference to Patch.bat

I missed a reference to patch.bat in commit
6d5aeb3607460ecf3a41947a0621862cb654c1de.
Substitute @...@ with ${...} in Patch.bat

This should improve readibility.
Add building packagest to build_desura.sh
Fix missing spaces
rename install-deps.sh to install_deps.sh for more consistency with build_desura.sh
install_deps: install binutils-multilib or binutils regarding of the system.
Move package to main directory
Merge pull request #480 from matthiaskrgr/install_deps

Install deps
Change build dir for packaging
Cleaning pack()
cmake: desktop dir is "/usr/share/applications"
cef: install libffmpegsumo.so

fixes #136
Merge pull request #481 from makson96/build_deb_rpm

Add pack_deb/pack_rpm option to build_desura.sh
cef: install media libs into seperated directory

having a lib directory in a runtime lib directory is just confusing. We
should also seperate runtime libs needed by cef from the one needed by
desurium itself
Merge pull request #485 from karolherbst/desktopdir

cmake: desktop dir is "/usr/share/applications"
Merge pull request #486 from karolherbst/bug136

cef: install libffmpegsumo.so
Check for patch on all systems

Ensure patch is available (and exit with an error if it can't be found).
Move patch.bat into CMAKE_GEN_SRC_DIR/scripts