[PM] Case conversion short cuts (Ctlr+U and Ctrl+I)

Most of the editors have this short cut to convert selected text's case. `Ctrl + U` to upper case and `Ctrl + L` to lower case. But already, `Ctlr + L` has been assigned to "Select Line", so i used `Ctrl + I` for lower case  conversion. Let me know, if you like this short cut.