[ModSupport] Improve performance for applying mods

[shoushou1106]

• Change ThreadPool to Parallel.ForEach
• Add MaxDegreeOfParallelism to config

ThreadPool will cause lagging because computer are not powerful enough to support that many threads
But this may require more test results, here are the results on my computer

Computer with SSD

Test game: GW2

ThreadPool(Original): 33s (very lag)
Parallel.ForEach(2 Thread): 32s (no lag)
Parallel.ForEach(1 Thread): 32s (slight lag)
Parallel.ForEach(4 Thread): 40s (very lag)

I will test on computer with HDD drive later