Add command whitelist/blacklist support

[devth]

Fix https://github.com/yetibot/yetibot/issues/988

• [x] if whitelist is configured, then everything is disabled except for whitelist commands
• [x] if blacklist is configured, then everything is enabled except for blacklist commands
• [x] if both are configured, error in the logs and quit
• [x] write documentation and update config samples

[codecov[bot]]

Codecov Report

Merging #133 into master will increase coverage by 0.37%. The diff coverage is 57.50%.

@@            Coverage Diff             @@
##           master     #133      +/-   ##
==========================================
+ Coverage   42.35%   42.72%   +0.37%     
==========================================
  Files          92       92              
  Lines        3936     3965      +29     
  Branches      175      178       +3     
==========================================
+ Hits         1667     1694      +27     
+ Misses       2094     2093       -1     
- Partials      175      178       +3     

Impacted Files	Coverage Δ
src/yetibot/core/webapp/route_loader.clj	35.29% <0.00%> (ø)
src/yetibot/core/hooks.clj	65.30% <41.66%> (-0.32%)	:arrow_down:
src/yetibot/core/util/command.clj	70.45% <65.38%> (-7.33%)	:arrow_down:
src/yetibot/core/loader.clj	85.71% <100.00%> (ø)
src/yetibot/core/commands/cron.clj	19.23% <0.00%> (ø)
src/yetibot/core/commands/history.clj	17.14% <0.00%> (ø)
src/yetibot/core/commands/observe.clj	14.75% <0.00%> (ø)
src/yetibot/core/commands/collections.clj	27.05% <0.00%> (+0.22%)	:arrow_up:
src/yetibot/core/commands/uptime.clj	63.63% <0.00%> (+27.27%)	:arrow_up:
src/yetibot/core/commands/decode.clj	90.00% <0.00%> (+50.00%)	:arrow_up:

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[devth]