Turn on ServerComputer instances if they have timed out

[SquidDev]

This is an attempt at solving parts of #95. It is not a complete solution. Namely, it solves the case where a server is running but has no one online.

Diagnosis

When a server has no players, some chunks (and so their tile entities) are kept alive but are not ticked. Consequently, each computer tile's ServerComputer times out and is removed from the registry.

When the chunk starts to tick again, the tile tries to find the ServerComputer. But, as this no longer exists, it creates a new one. However, it does not turn on this new computer (as the m_startOn flag is false) and so the computer remains off.

Solution

We add an additional flag m_fresh which determines whether a new ServerComputer has just been created. If so (and the computer was previously on) then this new computer will also be turned on when required.

Further notes

This shares some similarities with SquidDev-CC/CCTweaks#136. Whilst the fix implemented there is different, it should also fix this one (and vice versa).