fix: update storage issues

[joseivanlopez]

Problem

The list of storage issues is not correctly updated. The reason is:

• The storage monitor listens to the D-Bus PropertiesChanged signal in order to detect if the proposal has changed.
• If the proposal changes, then the monitor asks to the D-Bus proxy for the new list of issues, but the proxy might still contain the old cached data.

Solution

Change how the monitor updates the list of issues by directly listening to the D-Bus PropertiesChanged:

• When there is a PropertiesChanged with Issues, the monitor retrieves the issues from the signal instead of asking to the proxy.