Add Error Features for JS modules

[andistorm]

Add Error Handling/Reporting funcionality to JS framework

• Raise error: mod.provides..raise._('', '<severity')
• Request clear error by uuid: mod.provides..request_clear_uuid('')
• Request clear all error of one type: mod.provides..request_clear_all_of_type._()
• Request clear all all of module/impl: mod.provides..request_clear_all()
• Subscribe specific error type: setup.uses..subscribe_error._(subscribe_error_cb, subscribe_error_cleared_cb)
• Subscribe all errors of req: setup.uses..susbcribe_all_errors(susbcribe_error_cb, subscribe_error_cleared_cb)

Limitations:

• As it is not possible to register multiple handlers to subscribed var, it is not possible to subscribe multiple times to an error type

  Fix Everest::error::Severity

• Mid -> Medium
• Do not ignore set severity, but use it in Error constructor