Query groups

[icmx]

Currencies query must support groups, like this:

?by=USDEUR,CHFCNY,AEDAUD,CADAUD

Means just 4 "groups": USDEUR, CHFCNY, AEDAUD, and CADAUD

Plus symbol allows to configure a group:

?by=USDEUR,CHFCNY,AEDAUD+CADUSD

This means 3 "groups": USDEUR, CHFCNY, and AEDAUD+CADAUD

Each group should be treated as an array:

[
  [ 'USDEUR' ],
  [ 'CHFCNY' ],
  [ 'AEDAUD', 'CADUSD', ],
]

"Group" means that all the currencies must be rendered on one chart (or one converter row)

[icmx]

In UI this could be implemented by using "separation pill", like this:

(USDEUR) (USDCHF)        // no group for now

Now user types something like | and separation pill appears:

(USDEUR) (USDCHF) (||)   //two groups, second makes no sense now

Then user enters new symbol:

(USDEUR) (USDCHF) (||) (CNYJPY)

Which means:

[
  [ 'USDEUR', 'USDCHF', ],
  [ 'CNYJPY' ],
]