Template caching do not work #1378
Description
The cache for helpers.template do not work because it's declared inside the function scope and recreated at every helper call.
Also, only trivial variable-less template get cached (because of the !/\W/ regex).
This cause major slowdowns for charts that gets redrawn frequently (even in modern browsers like Firefox).
This can be fixed by changing a few lines (5, 21 & 37 in below gist)