Add deprecation notices to the deprecated docs

[chasenlehara]

All of these pages should have a deprecation notice:

• https://canjs.com/doc/can-component/beforeremove.html
• https://canjs.com/doc/can-component/content.html
• https://canjs.com/doc/can-component.prototype.events.html
• https://canjs.com/doc/can-component.prototype.helpers.html
• https://canjs.com/doc/can-component.prototype.leakScope.html
• https://canjs.com/doc/can-component.prototype.view-model.html

The deprecation notice should have the can-component version in which they were deprecated, a note about what APIs replace them, and ideally links to the migration guides for more information.

[cherifGsoul]

After discussion with @phillipskevin on Slack about the events replacements he suggested the add a section on events on the main Component docs and mention:

• normal DOM events
• “delegated” DOM events
• ViewModel events
• lifecycle events (inserted/removed)

Once is published we can add link to this page in the deprecation notice.