Minor fixes

[iamdefinitelyahuman]

What I did

• Allow use of timeout when adding new networks via CLI - fixes timeout not recognized as option from command line using 'brownie networks add' #531
• Add more expressive error when attempting to use Contract.from_explorer in a local environment

[codecov-commenter]

Codecov Report

Merging #533 into master will decrease coverage by 0.04%.
The diff coverage is 60.00%.

@@            Coverage Diff             @@
##           master     #533      +/-   ##
==========================================
- Coverage   88.44%   88.40%   -0.05%     
==========================================
  Files          56       56              
  Lines        6250     6259       +9     
  Branches     1380     1381       +1     
==========================================
+ Hits         5528     5533       +5     
- Misses        493      496       +3     
- Partials      229      230       +1     

Impacted Files	Coverage Δ
brownie/_cli/networks.py	76.64% <33.33%> (-0.67%)	⬇️
brownie/network/state.py	93.04% <60.00%> (-1.56%)	⬇️
brownie/exceptions.py	85.85% <100.00%> (+0.29%)	⬆️

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