Show warnings if JS is disabled or when the detected browser version is outdated

The Echo3 server-side implementation now adds a noscript-element
with a warning that shows when JavaScript is disabled in the user's browser.

A warning is shown at client startup when the detected browser version is considered outdated
by the current Echo3 client-side implementation (detected in Echo.Client._isBrowserOutdated).
The text of the default warning implementation Echo.Client.DefaultOutdatedBrowserWarning
can be configured using new 'ClientConfiguration' properties or substituted
by a new implementation analogous to WaitIndicator.