Allow path remappings in interfaces

[iamdefinitelyahuman]

What I did

Allow use of packages and path remappings when compiling interfaces.

How I did it

• Add the project.compiler.get_abi method. It uses the standard JSON input/output for compiling, similarly to how project.compiler.compile_and_format works.
• Mark the old vyper.get_abi and solidity.get_abi methods as deprecated.

How to verify it

Run tests.

[codecov-io]

Codecov Report

Merging #495 into master will decrease coverage by 0.01%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #495      +/-   ##
==========================================
- Coverage   88.33%   88.32%   -0.02%     
==========================================
  Files          56       56              
  Lines        6097     6106       +9     
  Branches     1341     1343       +2     
==========================================
+ Hits         5386     5393       +7     
- Misses        489      491       +2     
  Partials      222      222              

Impacted Files	Coverage Δ
brownie/project/compiler/solidity.py	92.30% <ø> (ø)
brownie/project/compiler/vyper.py	92.92% <ø> (-1.77%)	⬇️
brownie/project/compiler/__init__.py	92.00% <100.00%> (+0.51%)	⬆️
brownie/project/main.py	90.24% <100.00%> (ø)

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