Build against dependencies without root access

[Ryanf55]

Hello,

Nice work on this library. I'm interested to use it in a ROS 2 environment.

As part of the dependency install in install_deps.sh, it's calling sudo make install on some libraries such as g2o and openvslam.
I would prefer not to install some of these llibraries on my system with root permissions.

Ideally, a well behaved CMake project should obey the following workflow without errors.

cd g2o
cmake -B build
cmake --build build
cmake --install build --prefix install

This results in a local installation in the local install directory.
g20 does not respect the install prefix, so it could be patched.

Alternatively, OpenREALM can pull its dependencies in through the CMake build system without installing them through tools such as FetchContent.

Would you be interested in this method?

Longer term, I'd like to use this in ROS 2 with ArduPilot.

Upstream: RainerKuemmerle/g2o#885