reduce only

[c40003141]

• TP/SL --> ensure that they are posted as reduce-only orders // only on line 269 & 287 of ActionBlock? What about modifications through position table
• if reduce-only box is ticked by user for limit & stop orders, disable the option to choose TP and SL orders (none is selected by default and cannot be changed)
• - update "exceeding" logic for the case where (combined) order size > position size:
  a) if 1 reduce-only order with order size > pos size --> show price (instead of exceeding),
  b) if multiple reduce-only orders with combined order size > pos size --> show "multiple" (instead of exceeding) ,
  c) if multiple orders (reduce-only and normal) with combine order size > pos size, check if min(combined reduce-only order size, pos size) + normal-order-size > pos. size --> if true show "exceeding", if = pos.size, show "multiple" (if > pos size, continue to show partial).

[viktors-ovcinnikovs-verum]

PR: #481