Improve self-service dashboard widget localization (at least for "Edit" button))

Dashboard widgets (which are primarily intended for end-user rather than administrative use) should allow for more direct localization on buttons and other common strings. The "Edit" button, for example, makes use of the central "op.edit" language key which is valuable from the perspective of reuse - but in practice makes it difficult to change the string for the widget to something different. A change to the "op.edit" string - from "Edit" to "Manage" for example - would impractically change this across the application.

Change dashboard widgets, where appropriate, to make use of local strings rather than global ones so deployers can target the widget for localization (text) changes that won't impact the entire system.

It's an open question as to whether all dashboard strings should be local to the plugin. For now, make the "Edit" string local.