Fixed and improved URI compression

I fixed and improved your suggested URI compression:
* Instead of using base 2 for upgrades (which goes wrong for multi-staged upgrades), the code uses a dynamic base determined by the maximum of the current build (which goes up to base 5).
* Introduced the biginteger library by Silent Matt because some builds don't fit into Javascript's native ``Number``.
* Instead of using ``convArray``, I added custom ``stringToInt`` and ``intToString`` functions that work up to base 62 - similar to ``convArray``.
* I changed some of the ordering of decompression to avoid checking ``if (order)`` multiple times.