Peek in segment tab

Move peek 2D functionality to peek.js

FX_fcn.cpp: always erase customMappingTable if non existent ledmap

wled_server.cpp: add peek.js

index.js:
- add canvasPeek
- change resize of canvas

wled00/FX_fcn.cpp

@@ -1973,8 +1973,8 @@ void WS2812FX::deserializeMap(uint8_t n) {
   }
 
   if (!isFile) {
-    // erase custom mapping if selecting nonexistent ledmap.json (n==0)
-    if (!n && customMappingTable != nullptr) {
+    // erase custom mapping if selecting nonexistent ledmap.json (n==0) //WLEDM always erase if nonexistant
+    if (customMappingTable != nullptr) {
       //WLEDMM: if isMatrix then not erase but back to matrix default 
       if (isMatrix)
         setUpMatrix(true);