The server already includes such check. There must be a desync issue that causes
an ID mismatch, resulting in client crashes. Any such crash must be prevented.
This should improve compilation speed.
Things changed:
* Prefer forward-declarations in headers.
* Move header-includes out of headers if possible.
* Move some functions definitions out of headers.
* Put some member variables into unique_ptrs (see Client).
Fixes some other third person camera specific attachments.
Implements a single new flag for entities to be forced visible in first person mode.
Old mods do not need to be updated to use the new flag and are fully backwards compatible.
This commit clarifies the maximal length of the serialized strings.
It will avoid accidental use of serializeString() when a larger string can be expected.
Removes unused Wide String serialization functions
