Improve validator

[joachimmetz]

• check for key paths starting with %current_control_set%
  • Change behavior %%current_control_set%% #120
  • currently non-fatal fix GRR to support CurrentControlSet
• Warn that '%%users.homedir%%\AppData\Roaming can be replaced by %%users.appdata%%
• Warn that '%%users.homedir%%\AppData\Local can be replaced by %%users.localappdata%%
• enforce naming conversions
  • document artifact definition naming convention #25
  • add legacy indicator for GRR compatibility in legacy.yaml
• warn about use of **
• check for trailing whitespace
• add check to see if GRR and plaso dependencies are broken
  • https://github.com/ForensicArtifacts/artifacts/wiki/Dependencies
• Artifact Sources deprecated fields #181
• move HKEY_CURRENT_USERS check(

  artifacts/artifacts/source_type.py

  Line 279 in 8f526d1

  if key_path.startswith(u'HKEY_CURRENT_USER\\'):

  ) to validator
• change validation test not to use validator tool and remove __init__.py from tools
• check path expansion variable (Fix typo environ_programfiles86 -> environ_programfilesx86 #301)

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