Transitory GWT errors should be eventually cleared

Currently, any generated errors (shown at the top of the page) remain there 
forever. This is undesirable, because:

1) The user cannot discern between a stale error message and the same error 
caused by a more recent action.

2) The error is highly visible and is therefore distracting.

A few proposed fixes are:

1) The error should be placed next to the offending element that caused it, 
when possible. That is, the top level error should be used only for generic 
errors (e.g., could not contact the Synoptic server).

2) The top level error should have a less intrusive style. It should still be 
highly visible, but not as distracting.

3) All errors should be periodically cleared. Localized errors will differ in 
their clearing timing based on specific semantics. The top level error should 
probably be cleared whenever the user invokes an RPC (e.g., communicates with 
the server).

Original issue reported on code.google.com by bestchai on 13 Nov 2011 at 5:55

chubbymaggie / synoptic

Transitory GWT errors should be eventually cleared #150