Update "prob_type" CV

[agstephens]

The "UKCP18_prob_type.json" file needs a better structure. Please change the list structure into a dictionary with contents such as:

{
    "percentile":{
            "label":"Percentile",
            "description":"The value below which a specified percentage falls."
}

Add a similar section for the "sample" prob type.

[charliepascoe]

Added "sample" section to prob_type vocab.
Assumed sample data is for:

• one location
• one emission scenario
• one time period

Added lists of administrative regions and river basins used in UKP09. Added time periods and emission scenarios from the UKCP18 dataset spreadsheet https://docs.google.com/spreadsheets/d/1oNmJAYLGt6UrenY8XH_4gTyZGlFVW9plgyK75L3BN0Y/edit#gid=969822144

Info will need to be reviewed by UKCP18 team at the Met Office.

[charliepascoe]

Updated with simplified info. Note that I have used the UKCP09 definition of sampled data in the description field. http://ukclimateprojections.metoffice.gov.uk/22563

The "sample" description will need to be reviewed by the UKCP18 team at the Met Office.

"The sampled data provides 10,000 samples, each of which represents a projected change in climate for one location, emission scenario and time period"

[agstephens]

Done