[Feature] Skin engine Themes grab text from a file %ft(file, line) WIP

allow the skin engine to read text files and return a particular line

you then can use ss on that string to allow display of strings from the file
(Playername comes to mind)

able to be used as conditional
%?ft(filename)<Found|Not Found>

if (selected) line of file is empty the tag is treated as #COMMENT

scroll timeouts now persist thru trackchange

bugfix:
%t(n)%?x<text|text>
would ignore the specified timeout defaulting to 2 seconds

playername.txt generated at boot if it doesn't exist contents: 'RockBox!'

Change-Id: I961910e01be052ef902f77e6d92fc3e367ffe9d0

utils/skinupdater/tag_table.c

@@ -70,6 +70,7 @@ struct tag_info legal_tags[] =
     { "fn", "" },
     { "fp", "" },
     { "fs", "" },
+    { "ft", "" },
     { "fv", "" },
     { "d"  , "I" },