Fixed issue with incorrect estimation of entering canvas in viewport
Added timeout for check if element is entered in viewport
Escape double quotes to make proper string
Merge remote branch 'origin/safin/loader-viewport-issue' into rc3.0.20
Merge branch 'rc3.0.20' into neurostep/retry_canvas_fetching
[Utils -> retry] update logic to use exponential backoff algorithm, add tests;
[Echo.Canvas] rename "fetchRetries" config parameter to "maxConfigFetchingRetries";
update documentation