Create a visual difference between sid/stable and debug/general builds

[Feodor0090]

"[]" in about line in menu is not enough.

osu!'s example for inspiration:

[Feodor0090]

Possible direction:

• Define one more flag, "?sid".
• Add option in "build.sh" to filter them out.
• Build releases with filter enabled.
• Place red "DBG" text between softkeys in menu if debug version.
• Add "+" to version code if sid. Print it between softkeys too.