Parser: Auto detection of system proxy settings & bug fixes.

Bug fixes:
- Color state (RED) would be calculated for observations reporting OVX (horizontal visibility and cloud base are not present, but are still reported with 0 as value); the calculation of colour states for such observations are now omitted.
- Observations not having visibility or cloud base present, had their respective variables set to 0 instead of null, causing the colour state to be miscalculated.