Adapt to Camel's proxy resolver API changes.
Add EProxyComboBox.

EProxyComboBox is a combo box of available proxy profiles, as described
by ESource instances with an ESourceProxy extension.
Add EProxySelector.
Add EProxyEditor.
Add EProxyLinkSelector.
Add EProxyPreferences.
Use EProxyPreferences in EPreferencesWindow.

Replaces EMNetworkPrefs.