Save overhaul

[Geokureli]

continuation of #2566

Changes the FlxSave path

// from:
"C:\Users\<username>\AppData\Roaming\<app company>\<app title>\<localPath>\<name>.sol"
// to:
"C:\Users\<username>\AppData\Roaming\<localPath>\<name>.sol"

above example is windows, mac is similar and linux should be too (testing needed). If no file is found in the new path, the old path is loaded, but flush calls will save to the new location

Misc changes

• adds mergeData and isEmpty
• actually passes minFileSize to SharedObject
• FlxG.save only checks bind("flixel") if the new default bind is empty

Todos

• Test Linux cpp builds
• prevent creating the old "flixel" save for every game
• default localPath to company name (?)