Update thread names

[goeiecool9999]

Fixes #1013
I set out to change the main thread name to cemu like I suggested in #1116 and in the process I discovered that many threads did not get their proper names on Linux. The man page for pthread_setname_np states: The thread name is a meaningful C language string, whose length is restricted to 16 characters, including the terminating null byte ('\0'). This means that there are only 15 usable characters. Instead of cutting them off at 15 characters I decided to find shorter names. I opted to change the names for all platforms because having preprocessor macros would make things needlessly cluttered. I also discovered some nameless threads and named them.
The killall cemu command now works as expected.

Before patch	After patch