Extract canister configuration from dfx.json into separate files per canister

[ericswanson-dfinity]

Right now, dfx.json contains a top-level canisters object which defines the configuration of all canisters.

As canisters are added, this will concentrates a lot of configuration in one file. Also, this affords the opportunity to reduce some duplication of project names and directory paths.

We'll extract the per-canister configuration into separate files, referenced by dfx.json.

Design is now here: #889

Incomplete list of parts:

• Remove dfx config
• Read canister definitions either inline in dfx.json or from separate files
• When reading from separate files, make relative paths relative to canister.json location
• Make sure all paths are underneath dfx.json parent
• Decide if dfx new should generate files in inline or separate format
• Decide what to do about webpack

[kritzcreek]

Please ping me when this is about to land so I can make sure to update the VSCode plugin to chase down those configuration files. Thanks!

[p-shahi]

decided not to do this #889