* dvc: refactor config
Advantages:
- read like a dict
- modify as a dict for testing or manipulation purposes
- wrap modifications into context manager to save them:
with config.edit("local") as conf:
conf["core"]["remote"] = "new-default"
Design decisions:
- dropped string constants
- remote sections are parsed into a simple subdict upon load
- remote config schema is now defined by url scheme
- relative paths are handled transparently upon load/save
- user config and remote manipulations are moved to commands
- same dev manipulations are done by simply modifying a config dict
* test: do not set cache.type for remotes that doesn't support it
* dvc: fix windows absolute paths validation in config
* test: fix windows separate drive test
* dvc: stylistic fixes in config
Otherwise this will raise an exception from analytics worker:
```
dvc config cache.type sometypo
```
But running that same command with `--system` or `--global` flag outside
of repo won't raise that.
Also need to better handle ConfigObjError, but that is a separate issue.
Alexander Schepanovski
Ruslan Kuprieiev
pawel
Mr. Outis
Ruslan Kuprieiev