Introducing `AdminPagePreBuild` delegate

This delegate is needed in some cases in order for extensions to do things before the content pages (JSON/XML/...) are instanciated. Using `AdminPagePreGenerate` was not working in some cases because the `view()` method (where most of the code for content page goes) is called by the `build()` method called in `__buildPage`.
Fixed #2235
Publish filtering count

Fixes #2129
Update filter help on input

Fixes #2241
Merge pull request #2243 from jensscherbl/#2235

Allow pagination parameters to support the `dot` notation of parameters. Closes #2235
Merge pull request #2238 from DeuxHuitHuit/pre-build-delegate

Introduce a `AdminPagePreBuild` delegate
Clean-up styles
Merge branch 'integration' of github.com:symphonycms/symphony-2 into integration
canPublishFilter should follow canFilter hints
Some simplification to getFilteringFields
Add time and calendar settings to date field

See #2002
Create calendar interface

See #2002
Select date from calendar

See #2002
Calendar interactions

See #2002
Highlight active day

See #2002
Add calendar styling and interactions

See #2002
Merge branch 'integration' of github.com:symphonycms/symphony-2 into integration
Calendar improvements

- better element positioning
- focus current date
Calendar documentation
Publish Filtering and Empty Sections

Fixes #2246