Adding bare and json outputs to license command

[nicholasks]

• Removed the required from the --key because we should use a local db without it. But we still validate it when --db is not being provided.
• Added --bare to license command, which will only report the licenses names from the packages set.
• Also added the --json to license command, which will report the packages licenses as JSON. When a license is not available it will display as N/A.

[codecov[bot]]

Codecov Report

Merging #332 (b27a273) into master (23ac3a3) will increase coverage by 2.70%. The diff coverage is 77.77%.

@@            Coverage Diff             @@
##           master     #332      +/-   ##
==========================================
+ Coverage   68.88%   71.59%   +2.70%     
==========================================
  Files           8        8              
  Lines         495      514      +19     
==========================================
+ Hits          341      368      +27     
+ Misses        154      146       -8     

Impacted Files	Coverage Δ
safety/cli.py	56.63% <50.00%> (+6.63%)	:arrow_up:
safety/formatter.py	56.29% <93.75%> (+4.46%)	:arrow_up:
safety/safety.py	92.96% <100.00%> (ø)
safety/util.py	80.39% <0.00%> (+2.94%)	:arrow_up:

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