urlencode accessToken bugfix

We found that some services, for example *wkhtmltoimage* in our case, are using urlencoding functions.
When it goes to IMBO, `[` and `]` elements are replaced by `%5B` and `%5D` respectively.
It is then checked against accessToken, and doesn't fit it, as checksums of 
`... 572806?t[]=crop%3Ax%3D143%2Cy ... ` and 
`... 572806?t%5B%5D=crop%3Ax%3D143%2Cy ... ` are different.

We solved it by making simple `str_replace` in `QUERY_STRING`,  but it doesn't seem to be good solution for official version.
Probably better would be some changes in IMBO encoding or counting checksum.