Allow whitespace around origin list in config page

[agentgonzo]

At the moment, if you try to configure the allowed origins section of the plugin with http://foo, http://bar, then it will add " http://bar" (note the leading space) to the list of allowed origins. When a request comes in from "http://bar", it will not match (due to the whitespace) so the plugin won't add the CORS header.

[agentgonzo]

@uaarkoti @escoem - can you take a look at this please and merge if good?

[escoem]

hey @agentgonzo I'm not maintainer of cors filter plugin