sheetr/lexicons: Change from "system" to "character"

Signed-off-by: Naomi Roberts <[e-mail]>

lexicons/system/dnd5e/system.json lexicons/system/dnd5e/character.json

···
 {
   "lexicon": 1,
-  "id": "app.sheetr.system.dnd5e",
+  "id": "app.sheetr.system.dnd5e.character",
   "defs": {
     "main": {
       "type": "record",
       "key": "tid",
-      "description": "A system for Sheetr to support D&D 5th edition.",
+      "description": "A character for D&D 5th edition.",
       "record": {
         "type": "object",
         "required": [],