Update Ceres from 1.14.0 to 2.1.0

[willdunklin]

Notable changes:

• Added option to enable C++17 which is on by default
• Change fallback C++ standard to C++11 from C++98
• Update CMake minumum required version to 3.10
• Update Ceres from 1.14.0 to 2.1.0
• Update GLog from 0.3.5 to 0.6.0
• Update SuiteSparse from 4.4.5 to 4.5.6
• Remove libjson from Fletch