Add TFCond & TFCollision as consts

[Kenzzer]

Partially completes #1618
Takes over #497

As discussed in #497 this PR adds the entire ETFCond enum as const variables in tf2.inc + TFCollision enum.
PR also deprecates gamedata usage for TFHoliday values and instead grab the ones from hl2sdk.

[Kenzzer]

@psychonic I assume you're holding off on a review because of your concerns around switch statement right ? Should this be a feature request over sourcepawn repo ? allowing usage of const variables in switch statements ? I genuinely realise this is far easier said than done, SP has quite the amount of quirks surrounding its variables.