implement option for custom security check for views

[sgratzl]

e.g. whether the user has a certain role

.security(lambda user: user.has_role('role_name'))

[sgratzl]

added options:

server side: DBViewBuilder.security(rolename|(user)=>boolean)
client side: part of tdpView extension definition: security: (rolename|(user) => boolean)

zB

 .security('admin')
 .security(lambda user: user.has_role('admin'))

  security: 'admin'
  security: function(user) { return user.roles.indexOf('admin') >= 0}