Error boundary

[maraf]

Evolution of #285.

• Current implementation of tag exception processing is not correct. One can't define which tag can and which can't swallow exceptions and continue page processing.
• I'm thinking about introductions of "error boundaries".
• Let any tag exception fail whole page.
• Let template author decide which group of tags can transiently fail.

...
<!-- Error boundary -->
<error:boundary name="main">
    ...
</error:boundary>

<!-- Show error details -->
<web:out error:boundaryFailed="main">
    <error:exceptionList name="main"> <!-- Optional filter -->
        <ui:forEach items="error:exceptionList">
            <pre>
                <web:out text="error:exceptionType" />
                <web:out text="error:exceptionMessage" />
                <web:out text="error:exceptionTrace" />
            </pre>
        </ui:forEach>
    </error:exceptionList>
</web:out>

<!-- Show if boundary passed -->
<web:out error:boundaryPassed="main">
    ...
</web:out>

<!-- Shorthand for development details and standard "500" view -->
<error:exceptionView name="main" />

TODO

• [x] Drop try-catch from template parser
• [x] Drop edit model support for exceptions
• [x] Error boundary
• [x] Option to skip logging the exception
• [x] Extra params for log.
• [x] Error list
• [x] Failed decorator
• [x] Passed decorator
• [x] Default exception view
• [x] Default boundary in Web::processRequestNG (aka 500)