[webapp] Provide users a way to easily find errors and keywords in logs

[mwfarb]

Currently SCIONLab users who are trying to resolve issues or attempt to educate themselves on the operation of SCION may hunt through logs for information. The Health Check and troubleshooting guide proactively provide insight to common configuration issues, however it would be great to provide users a way to navigate unexpected errors and generally monitor healthy operation.

The webapp could provide a Logs tool to graphically and textually show logs from all services, routers, daemons, and dispatcher to:

• highlight warnings/errors/critical errors and stack traces
• allow users to select a highlighted issue and show the location in the logfile for greater context
• provide an index of running services
• monitor general operation of the AS
• display errors graphically by time as well as linearly.

Questions to answer:

• Are there other open source tools that do the above, or should be write it?
• Does this tool already exist for SCIONLab users in the form of logdog?

[mwfarb]

Additional considerations from discussions:

• This tool should be built to be used independently from scion-apps and scion-coord.
• It can also be incorporated into a tool like webapp.
• Add good filtering and aggregation: show first and most recent occurrence.
• Add defaults that recognize logs are noisy and many things are logged as error.

[mwfarb]

This could be simplified by adding a panel below the AS Topology graph on the Monitor page added in #122, such that it would display the log tail and allow scrolling of the log for the service clicked on the graph.