Fix/simple dex testcoins

[smk762]

Closes https://github.com/KomodoPlatform/komodo-wallet-desktop/issues/2369

To Test (pro view):

• Select DOC in the left combo selector on dex pro page.
• Select MARTY in right combo selector on dex pro page.
• Click on an order in the orderbook
• See only testcoins listed in bestorders box

To Test (simple view):

• Select DOC to sell in simple dex view.
• Enter a value to sell
• Expand the buy coin selection list
• See only testcoins listed in buy coin selection list

Inverted test (pro):

• Testcoins should also be excluded from bestorder response for coins with value. I've set up a maker order for MARTY -> PANDA to help test this.
• First confirm the PND/MARTY order exists. If it doesn't, pinf me and I'll create another one.

• Next, select PND in left combo in pro view, and click on an order in the orderbook to show the bestorders.
• MARTY should be excluded from the list.

Inverted test (simple):

• Select PND to sell in simple dex view (if you have no PND balance, do a small trade to get some, its cheap).
• enter an amount to sell to activate the buy section.
• Confirm MARTY does not appear in the buy coin selection list.
  

NOTE: Pro view has since been updated to the new tabbed orderbook/bestorders layout, so the screenshots above are indicative but not how app currently looks. Updated view below for reference.

updated-view.mp4

[AndrewDelaney]

Testing successful. Items tested:

• (Pro) Swap 2 Test Coins: Confirmed only test coins are displayed in Best Orders
• (Simple) Select Test Coin to Trade: Confirmed only test coins are displayed for available trades
• (Pro) Swap Coin with Value: Confirmed test coins do not show in Best Orders
• (Simple) Select Coin with Value: Confirmed test coins are not displayed in available trades
• General wallet functionality is unaffected
• UI functionality is unaffected