Feature: provide UI for reporting important SAFE related errors

[happybeing]

This feature is needed because there is no easy way to report the cause of errors such as insufficient account balance.

Many errors can just be reported through the file system interface, such as "File does not exist" as normal, but some important SAFE errors are not catered for by the FUSE / POSIX error codes, and we need a way to cater for these. Examples are:

• insufficient account balance when mutating a file, creating a file container, public name etc.
• reason for last authorisation request that was rejected

Please use this issue propose or provide feedback on what's needed and how to implement it.

I think a related issue which needs a UI is to allow access to status information, but for this there are more options. See also #8

Ways to Report Important Errors

We want to alert the user to the problem as soon as possible, because it won't be apparent if all we do is fail the operation. We also want a way for the user to check the status of important error conditions in case they miss any notification.

So for something like 'insufficient account balance' we might:

• alert the user via the host OS notification mechanism (I'm not sure how feasible this will be - but it is probably preferable to only using a 'phantom file' approach (see next). It might also combine well with a mechanism for accessing status such as account balance, SAFE Network status, etc
• cause a 'phantom file' to appear in every listing of a directory to indicate there's an important error. The name of the file could describe the problem (e.g. "Error insufficient account balance to save data"), which would disappear as soon as a successful write occurs).
• any other ideas?