Remove memory limit for PHP scripts when running chef.
Optimizations regarding page loading:
- `PageRepository` is now keeping all pages around, but listens to those being loaded.
  Recycling is done by unloading older pages when too many are loaded.
- Added `IPageObserver` API.
- Added `PageInfo` and `PostInfo` for file-system information, instead of using dictionaries.
- Changed how post dates are access to minimize the situations in which they have to be loaded.
- Optimized `CachedEnvironment`'s page indexing.