tab clone in tag: user.tabs (#1457)

I propose to allow users to also say "tab clone". This would make the
command consistent with rango. This will become particularly useful
once/if community has more applications/contexts that support the "tab
duplicate" voice command. Background: I was planning on implementing the
command for windows explorer.

To enable compatibility with rango I also created a complementary pull
request on that repository: [PR
13](david-tejada/rango-talon#13)

core/windows_and_tabs/tabs.talon

@@ -7,4 +7,4 @@ tab close: user.tab_close_wrapper()
 tab (reopen | restore): app.tab_reopen()
 go tab <number>: user.tab_jump(number)
 go tab final: user.tab_final()
-tab duplicate: user.tab_duplicate()
+tab (duplicate | clone): user.tab_duplicate()