Refactor and improvements on command

Check available helpers
Default permission: view only
Moved validate setting from helper to command
Turn more easy create a importer
Docblock and improvements on interface
lcfirst on system property
Helper moved to ImporHelper folder
Moved fixtures to ImportHelper
Rename settings to config
Big refactor to move import methods to service

Signed-off-by: Vitor Mattos <vitor@php.rio>

lib/Command/ImportHelper/fixtures/config-trello-schema.json

@@ -0,0 +1,24 @@
+{
+    "type": "object",
+    "properties": {
+        "uidRelation": {
+            "type": "object",
+            "comment": "Relationship between Trello and Nextcloud usernames",
+            "example": {
+                "johndoe": "admin"
+            }
+        },
+        "owner": {
+            "type": "string",
+            "required": true,
+            "comment": "Nextcloud owner username"
+        },
+        "color": {
+            "type": "string",
+            "required": true,
+            "pattern": "^[0-9a-fA-F]{6}$",
+            "comment": "Default color for the board. If you don't inform, the default color will be used.",
+            "default": "0800fd"
+        }
+    }
+}