Removed unsafe usage of priority values

[WaCrex]

Changes:

• Removed unsafe direct usage of priority level, as a simple typo in the config file might cause havoc on the system.
• Inputting an invalid value will now default back to 4 (High).

These are the new values:	Priority	Value
Idle	0
Below Normal	1
Normal	2
Above Normal	3
High	4
Realtime	5

I've got precompiled binaries available for download in my fork if anyone want to test it on their system.