Do this by representing every float('inf') python numeric as a 1e+999
JSON token - this way Javascript JSON.parse() correctly transforms it
to the Javascript Infinity object. The infinity value corresponds to
disabled limits.
The logic of representing infinity values as 1e+999 tokens is
implemented by means of custom `NaNJSONEncoder` which overrides
`iterencode` method of its `json.JSONEncoder` ancestor. Due to the
fact that the ancestor method could take an advantage of
`c_make_encoder` function (which is implemented in C) - and thus could
be much faster, I'm using the custom encoder only where it's really
needed, to not hamper Horizon performance.
Rewrite pie-chart directive rendering according to
https://invis.io/A4445BDSF
Change-Id: If498d9ccd5f0144c9e78ae58583ede2c1cf83f0b
Closes-Bug: #1482705
5398de264d