updating install script & instructions with CMake

See merge request !29

Defining the same classes in two shared objects confuses ROOT.

See DAS#121.

Newer CMake versions seem to always checkout the remote branch,
discarding local git information. Disable updating altogether so this
problem cannot appear. We will do updates ourselves.

See #15.

Also add a todo to get rid of it if we can.

This is needed to run prefix commands.

This is needed for File Sets support.

For now, use the branch from my fork to get things going. We'll update it
later.

It looked easier than writing a Find module.

Support users redirecting git https to ssh

See merge request !27

Multiple users complained that the installation wasn't working for them. They
were stuck with git asking for their SSH password and no way of providing it
since git is run through CMake.

Detect the configuration that leads to this issue and start the SSH agent if
needed, then register the user's main key with it. Try educating the user about
what is happening and that it's ultimately their fault if something breaks.

Move the Darwin binary dir next to Darwin

Closes #16

See merge request !26

Remove the Makefile and files it uses

Closes #12

See merge request !25

This allows rebuilding Darwin only with:

    cmake --build $INSTALLER_BASE/Darwin.build

Closes issue #16.

The Makefile build system was replaced by CMake, which uses a different
approach to create the xml files for darwin and tunfold.

Run "git lfs install" automatically for tables

See merge request !24

improving README and setup after seeing repeating misunderstandings from newcomers

See merge request !23

See Tables!10.

Bugfix/crab

See merge request !22

fix patch application

See merge request !20