Consolidate components Actions and Event documentations.

[aghassemi]

Currently there are two places actions and events for each components are documented.

1- Majority are in https://www.ampproject.org/docs/interaction_dynamic/amp-actions-and-events
2- Some components duplicated or sumemrized a version in their own .md file in addition to above.

Some suggestions:
1- https://www.ampproject.org/docs/interaction_dynamic/amp-actions-and-events to focus on how to use events and actions.
2- Separate documentation for common actions ( similar to common attributes)
3- All components to document their actions and events inside their own .md file.
4- Maybe https://www.ampproject.org/docs/interaction_dynamic/amp-actions-and-events can point to common and component actions as links?
5- Maybe the table on top of each component file can list attributes, events and action names same way it does for layouts for a quick overview?

[sebastianbenz]

//cc @CrystalOnScript we definitely should look into how we can improve this.