Pgrohe/issue969

Pull request for changes to core/main/client/dom.js as discussed in [Issue #969] (https://github.com/beefproject/beef/issues/969).

After discussion in [Issue #969](https://github.com/beefproject/beef/issues/969) it was decided that the 'method' parameter of dom.createIframe() lacked clarity and that the parameter and the entire codepath that used it to decide whether to create and submit a form could be removed.

I removed the 'method' parameter of createIframe(), the conditional logic that used it and all the form generating & submitting code.

dom.createIframe() will now simply create an iframe tag , populate it's attributes and style properties, prepend it to the body and return the iframe element.

All existing calls beef.dom.createIframe() to remove the 'method' parameter which is no longer present in the function definition.  None of the existing calls to this function used the codepath that was removed so this was simply a matter of removing the 'method' parameter from the calling code.  The functionality which the existing calls were using is now the default (and only) functionality of createIframe().

The affected function calls are in the following files:
* extensions/customhook/html/index.html
* modules/browser/hooked_domain/site_redirect_iframe/command.js
* modules/social_engineering/fake_lastpass/command.js
* modules/misc/iframe_keylogger/command.js
* modules/exploits/local_host/java_payload/command.js