Issue 23: Added progress indicators and cancellation (#34)

- Wrapped all table operations in a new foreground job context, which mediates foreground tasks.
- Added cancellation support and partial results for table read operations.
- Added the "mark" command, which can mark, unmark & toggle marked items
- Added support for alias arguments.
- Removed the "unmark" command, and replaced it as an alias to the "marked" command
- Fixed seg faults raised when there is no table shown in the result set.

internal/common/ui/events/jobs.go

@@ -0,0 +1,6 @@
+package events
+
+type ForegroundJobUpdate struct {
+	JobRunning bool
+	JobStatus  string
+}