Unified network settings and removal of config file

[iamdefinitelyahuman]

What I did

This is a big one...

Related to the config file:

• remove requirement for a configuration file within a project - closes Reduce the config file #325
• reduce possible network settings to live and development and use sensible defaults
• add show_colors as an optional setting to disable colorful output

Related to networks:

• unify network settings across all projects on a machine!
• add brownie networks commandline interface for working with networks
• deprecate network settings in brownie-config.yaml

Also lots of documentation updates and new tests. Closes #376

How I did it

• In brownie._config, refactor how configuration settings are stored. CONFIG is expanded to an object that holds the configuration settings, cli arg settings, and network settings
• network settings are now stored at ~/.brownie/network-config.yaml - a warning is raised when a project has a config file with now-deprecated network settings
• A folder is considered a project if it has a config file, OR has both tests/ and contracts/ subfolders, OR has a contracts/ subfolder with at least one .vy or .sol file inside it.

How to verify it

Run tests.