LevelManager: Remove unneeded methods
TerrainEdit: Remove some unneeded variables
Serialization: Refactor PurgeDeleted() from DeserializeTypeMapOptional()

PurgeDeleted() update the instance list to remove the destroyed
object and return true if there was at least one object destroyed.
Serialization: If object that is need to be deserialized is null, log warning
Serialization: Take care of destroyed objects when deserializing

When deserializing, some objects could be destroyed. Need to handle
it. It log warning if this does happens.
TerrainEdit: Mark terrain manager dirty when terrain is created
TerrainEdit: Destroy GO, not component when deleting old terrain
TerrainEdit: Traverse all Terrain components when destroying the old terrain

We need to traverse all child Terrain components, not only this
referenced in terrain manager, because some others might still
exist but not referenced by terrain manager (because of some
exception thrown while deleting the old terrain in previous time).
Serialization: Always rebuild type map

It is better to have always up to date time map then to try to
resolve some missing types when caching it.
Serialization: #region names changes
Add code style document
MonoSingleton: Don't show error on creation
Serialization: Implement serialization optional post-processing
Serialization: Make the buffer for each to-be serialized objects

It is better to have each buffer for serialized object, because if
some of the objects are null when deserializing, could skip
deserialization. Also we could now implement selective serialization
of object.
ja2: Rename #region Attributes -> Fields
Map: #region clearance
Serialization: Support for explicit non-serializing attribute

Support for [NonSerialized] attribute to not serialize fields.
script: MapInstance isn't used anymore
Set some default scene when building
Editor: Custom scene change on play/return on stop

It will be used when testing dynamic level creation, when we want to
work on one scene, save the data, and the run the another scene in
which the level will be generated from data and then back to
edited scene.