Add backoff/retry logic to generate more intuitive repo export names
Add backoff/retry logic to generate more intuitive repo export names

Start with the page title, then increment and append a number to the
page title on failure. Before we used timestamp to guarantee unique
names but this creates shorter and more easily shareable names.

Fixes: #1476

jwang1919/popcode,jwang1919/popcode,popcodeorg/popcode,jwang1919/popcode,popcodeorg/popcode,outoftime/learnpad,jwang1919/popcode,popcodeorg/popcode,popcodeorg/popcode,outoftime/learnpad