Add other webOS asset images

[GA251]

(Refer to #373)
Currently, youtube-webos only provides a icon and a largeIcon, which means when you use the app, the assets listed below fall back to WebOS's placeholders:

These are the assets that are used in the YouTube official webOS app that do not have youtube-webos equivalents.
splashBackground (The splash screen when the app is being launched, webOS fallback is a static spinner icon, the official YouTube app just uses a gray background that matches the app's theme)
playIcon (Used in search results? - YouTube's official app uses a favicon)
imageForRecents (Used in the recent apps list)
bgImage (Have no clue what this is used for, maybe it is used in earlier webOS versions?)
mediumLargeIcon (Most likely used for HiRes/HiDPI displays)
extraLargeIcon (Most likely used for HiRes/HiDPI displays)

All assets were created by me.
Currently, the splashbackground has two variants:
Variant 1 (splashBackground-v1.png - default) is the gray background, with the same background color ensuring a smooth transition to the web app.
Variant 2 (splashBackground-v2.png) is a black background with the YTAF logo with a red shadow.

I'm not sure if the gray background tone is like copyrighted or something so I made another splashbackground one just in case.

SplashBackground Variant 1

SplashBackground Variant 2

[GA251]

splashBackground.zip
Forgot to add this, here is the PSD file for the splashBackground-v2 in case any tweaks are needed.
I recommend opening this in PhotoPea as the file was created using it.

[fire332]

Please clean-up the commit history. You should only have 1 commit named "add other webOS asset images" or something more identifiable. The commit names should start with a lower-case letter.

[FabioPedretti]

Note: you may also want to optimize the images size with oxipng -o max -Z, to save some space on the TV and downloads.

For example, bgImage.png is reduced from its original 28184 to 20333 byte.

[GA251]

I'll create a new PR with all the required changes as I accidentally force-pushed instead of cleaning up the commit history. sorry :(

[fire332]

Force pushing is actually what you need to do to clean up the commit history as you need it to overwrite history. Otherwise, git won't let you.

[GA251]

sorry bout that, not very experienced with github (or git in general)
had to create a new pull @ #384