logic: load 6 skybox textures when shader gets used by scene, don't unload dynamically, just on 'flush'
texture browser only uses normal preview image and doesn't trigger potentially heavy box loading
also fix R_ResampleTexture for [2+x upscaling
misc...
* texbro: disable alpha transparency by def; isn't good in half of cases
* find/replace: tooltip helper note about search mode
* Entity: arrowheads, showing direction of connection-lines in addition to color-code; New algorithm: are visible in all orthogonal projections
* tweak: do not render 'misc_model' & 'light' entity names
* filters: patches: +filter ones with surfaceparm playerclip
* translucent filter also works for shaders with qer_alphafunc
* filter areaportal, if single face matches (allows case with other faces, using 'skip')
* filter translucent, if single face matches
* filter liquids by surfaceparm {water, lava, slime} in addition to textures/liquids path
