Add "Display streaming FPS" option

[MakiseKurisu]

Currently the streaming FPS option is defined at build time. This PR aims to make this an end-user changeable option.
I'm currently working on display scaling for 21:9 host resolution, so I'm intended to add more diagnostic info to this feature later.

[mirh]

This is cool, but what kind of decent scaling could you even achieve between different aspect ratios?
Unless you are talking about proper 21:9 with the right fov, and scaling means pan and scan?

[MakiseKurisu]

The issue with 21:9 host monitor is two fold:

1. when host is running in 21:9 resolution, Moonlight will display a squeezed image on Vita's 16:9 display. In this case we need to squeeze the image again to add black bars on the top and bottom. As a bonus we can use the black bar to display extra info (fps, touchscreen special keys, ping, etc)
2. when host changes to a 16:9 resolution, Moonlight will still show a 21:9 squeezed image, with black bars on the left and right. In this case we need to desqueeze it.

When I say scaling I'm really talking about squeezing and desqueezing, and this can be done by replacing vita2d_draw_texture with vita2d_draw_texture_scale. Currently Moonlight will redraw menu in the black bar area, so I need to figure out how to disable that part of code during streaming.

[d3m3vilurr]

could you rebase it?

[MakiseKurisu]

Alright I think that's it. This is the first time for me to do a rebase from command line, so hopefully I didn't mess anything up.

[d3m3vilurr]

pretty mess, but it's okay. i'll squash these commits ;)

[d3m3vilurr]

9f27692