Review all bundle docs

[wouterj]

All bundle docs will need a quick read-through, fixing all sort of things before the 2.0 release.

• [x] block #830
• [x] content #824
• [x] core #816
• [x] menu #822
• [x] routing #814
• [x] routing_auto #833
• [x] seo #823
• [ ] sonata_phpcr_admin_integration
• [ ] tree_browser