[UX] Check for duplicate wallet/contract window

[ixje]

Each click on a wallet or contract opens a new window without checking if the window was already open.

The default file explorer of VSCode does not seem to open duplicate windows when clicking a file so this feels like deviating behaviour from the default.

[robliou]

_//Update as of 5/28/22- actually this issue is still open. The reason I thought I had this issue fixed was because I had changed my setting

"workbench.editor.showTabs": false

and this resulted in only one tab showing up at a time. However, this is true for all tabs, not just for wallet or contract. Therefore, the problem is still there. Will have to find another solution for this.
//_

I removed the activation event from package.json which was triggering a wallet and/or contract being opened in a new window every time a user clicked on a wallet or contract on the side bar. Now a wallet/ contract opens up only once in the same window, so should be much less clutter. Should double check to make sure that this is what we want. See commit below:

4634306