docs: improvements to Apport content #540

A new page on Apport was recently added to the docs. Aside from a general technical review for accuracy and currency, it can be improved in several ways:

• There are multiple links to old wiki pages and bazaar.launchpad URLs that should ideally be updated, replaced, or deleted. The wiki pages will eventually be deprecated and the bazaar pages are not found.
• One wiki page is cited prominently --- https://wiki.ubuntu.com/Apport/DeveloperHowTo --- and may warrant migration to the project docs, where it can be cross-linked.
• The section How to enable Apport should be updated to reflect that Apport is now available in the Control Center. UPDATE: closed by @RezSat in Update how to enable Apport to reflect availability in the Control Center #577