feat(Tumblr): Add Disable Tumblr Live patch

[leumasme]

The DisableTumblrLivePatch

• Changes the expected ID of the tumblr live dashboard/timeline carousel element to a dummy so the app will not recognize it (see feat(Tumblr): Add Disable dashboard ads patch #2979)
• Depends on FeatureOverridePatch to overwrite the value of an A/B testing feature flag to hide the Live tab button in the bottom navbar

The FeatureOverridePatch

• Adds a new helper function to com.tumblr.configuration.Configuration which accepts a Feature object and returns the overwrite value if one is present, or null if the feature should not be overwritten
• Hooks a method on com.tumblr.configuration.Configuration responsible for getting the string value of a Feature object to call the helper function and return its value instead if it doesn't return null
• Presents an addOverride(String name, String value) delegate method which adds the equivalent of
  if (currFeatureName == {name}) return {value}; in the middle of the helper function. This is currently only used once, but has been tested to work with multiple feature overrides.

The FeatureOverridePatch is not registered as a @ Patch since it is not usable by itself. A patch options screen could be added in the future to let the user set custom feature overrides, making the Patch indepentently usable.