Strip symbol wrappers

[jagrg]

M-x helm-apropos fails to preselect the correct symbol at point when wrapped with the = or ~ characters. This patch makes helm-apropos smarter in Org derived modes by stripping the wrappers before returning the symbol name. Some examples:

mu4e-mailing-lists  =>  mu4e-mailing-lists 
~mu4e-mailing-lists~  =>  mu4e-mailing-lists
=mu4e-mailing-lists=  =>  mu4e-mailing-lists
mu4e~headers-mark   =>  mu4e~headers-mark
~mu4e~headers-mark~  =>  mu4e~headers-mark
~M-x mu4e-quit~    =>  mu4e-quit
=M-x mu4e-quit=   =>  mu4e-quit