Refactoring ExtLibraries structure

[sksat]

Details

Currently, ExtLibraries is very diffitcult to setup, understand, and maintain.

• Directory naming conventions are out of sync with normal S2E directories
• Duplicate responsibilities with src/library/external
• Hard-to-manage external libraries with CMake
• Downloading files from the Internet with CMake
• Downloading data files (these are NOT library) from the Internet (with CMake)
  • Both build-system & runtime should be know ExtLibraries path
• Out-of-repository install destination (../ExtLibraries)

Closing conditions

After renaming ExtLibraries or reorganizing its structure

Supplementary information

Provide any supplementary information.