Content: ACF Expression2 Extension

Added some E2 functions relating to various ACF entities.
-Search "acf" in e2helper for a complete list and description of
functions.
-Includes the convar "sbox_acf_e2restrictinfo" that restricts certain
functions (generally those that return sensitive data) to usage on owned
entities, preventing abuse during battles. Defaults to 1 (restricted).
-Functions that change values, e.g. gearbox shifting, are permanently
restricted to owned entities.
E2 Extension: Engine info checks

Added restriction checks to some engine functions.
E2 Extension: Gearbox info checks

Derp, should have added these in while I was at it.
Merge pull request #15 from Fervidusletum/E2_Extension

Content: ACF Expression2 Extension