better method to activate leaf

• used a better method to activate leaf
• resolved issues raised in this comment

`open panes` view added

initial changes:

• added open panes view
• removed 'reveal tab' commands since they were rolled into core

as of [2021-04-26]:

• changes suggested in PR comment

initial release

features

• pin/unpin all leaves
• reveal workspace-tabs (tag-panel, backlinks, outline, etc.)
• reveal some plugin tabs (recent-files, calendar, etc.)