YAML configuration

[yoctoyotta1024]

Use YAML libraries to write and read in CLEO configuration rather than .txt files:
major:

• include yaml-cpp external library in cmake build
• replace every config .txt file with equivalent .yaml file
• pass new config to constructors in main programs
• re-write pySD functions for reading config in python using ruamel.yaml package

minor:

• some re-naming of variables e.g. W_AVG ->W_avg
• better choice of types for some config variables e.g. string -> filesystem paths
• distinction between optional and required configuration variables. Optional are only needed for som model setups whereas required are always needed.
• configuration of independent things held in individual structs, e.g. condensation variables contained in YAML condensation node are saved in config.optional.condensation member