[CoreBundle] Added mailer for emailing quotes and invoices
[QuoteBundle][InvoiceBundle] Made discount nullable
[ClientBundle] Make contacts cascade when saving
[CoreBundle] Use the logged-in users email address when no from address is specified
[SettingsBundle] Remove unique constraint on settings key
[SettingsBundle] Update settings to allow settings type and options (see CustomScripts/SettingsBundle#0ae109)