Knight changes!

- Darkness skill is now a Critical Damage buff

- Light and Darkness skills are now solely based on END

- Light and Darkness points gained per kill is now based on END instead of SPR

- Light and Darkness buff icons' has been replaced

Development note: 

- In addition to the past changes, We've decided to copy the behaviour of the SPR on Mages to the END for Knights, adding the entire Light and Darkness damage bonus to the END, leaving the fully Physical Damage to STR.

- These changes will help a lot to those players who want to go for new builds, and also bring a boost of Critical/Physical Damage for all Knights who are currently using the main build.