feat: disabling UI

[dan-ziv]

Description of the Changes

Created a UI wrapper using the proxy pattern, which all the UI actions will pass through it.
UI can be disable using the following configuration:

ui: {
  disable: true
}

CheckLists

• changes have been done against master branch, and PR does not conflict
• new unit / functional tests have been added (whenever applicable)
• test are passing in local environment
• Travis tests are passing (or test results are not worse than on master branch :))
• Docs have been updated

[kaltura-hooks]

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[dan-ziv]

build failing is not related to this change, merging