Support opening leo files from explorer pane and offer 'recent files' along with auto opening

[boltex]

Try to add an entry in the regular explorer (right-click) files context menu if a file has extension ".leo"

(Idea given after reading Brad's comment on the google group forum about having more 'seamless' integration.)

Note: The user must have had set his leoInteg settings correctly to automatically "start server" and "connect to server" and optionally 'python command' launch string at minimum for any of the smooth integration to even make sense in the first place.

[boltex]

In the same vein, as suggested by Edward, a 'recently opened Leo files' accessibility would be desirable.

Try to find ways, or places in the U.I. (menus, lists, ...) where this could be inserted or implemented.

[boltex]

ALSO : maybe reopen automatically the Leo files that were opened in the last session when it was closed.

[boltex]

Summary (3 Items):

• Right click -> Open with leoInteg
• Recent Files Command that opens a 'quick pick' menu, which in turn opens the file chosen from it upon selection
• (Automatic Function) Upon connecting to leoBridge: Reopen last opened files. (Not all recent files list, just files that were opened when last vscode session finished)