sim-cli/bug: Interaction between simulation file path and results directory

[alexzaitsev]

Addressing #217
Logic:

1. If sim file is present (absolute or relative, doesn't matter) - use it.
2. If it's not present as it is - fallback to the current behaviour:
   a. try to join with data_dir, if it's present -great
   b. if it's not present - fallback to datadir lookup
3. If it's neither present of relative path - fallback to datadir lookup.

[carlaKC]

tACK 94f56c6, such a nice UX improvement 🥇

Cases tested:

1. Custom sim file and custom data dir: sim-cli -s custom_sim.json -d custom_data_dir/

custom_sim.json
custom_data_dir/

2. Custom sim file in custom data dir: sim-cli -s custom_sim.json -d custom_data_dir/:

custom_data_dir/custom_sim.json

3. Default sim file in custom data dir: sim-cli -d custom_data_dir

custom_data_dir/sim.json

---

The only this that could be confusing with this UX is if you have a sim file with the same name in multiple locations, eg:

duplicate_sim.json
custom_data_dir/duplicate_sim.json

sim-cli -s custom_sim.json -d custom_data_dir/ will use the one in the current directory, which I think is the right decision.