Fix bad API_KEY handling.

There are a number of issue detected with the current handling of the API KEY:

[x] CLI seems to try to send the auth token of a parent org when making actions on a child org.
[x] CLI writes config with 0644 permissions on user's home which is bad (fix perm)
[x] If the config is empty, the CLI panics (bad errors handling and nil map assignment)
[x] We should allow (and recommend) to fill in the token via env var. Passing the token via arg will write it in the user's bash history.
```
### Tasks
```
[ ] Scope login to API URL
[ ] In the config file, split orgs by API URL
[x] If the config is empty, the CLI panics (bad errors handling and nil map assignment)
[x] CLI writes config with 0644 permissions on user's home which is bad (fix perm)
[x] We should allow (and recommend) to fill in the token via env var or stdin. Passing the token via arg will write it in the user's bash history.
[ ] Org related token env
[x] Fix current org selection via config / env var

cycloidio / cycloid-cli