Improve pagination for openqa-mon

[grisu48]

Add some minor improvements to the pagination feature:

• Display page count from the beginning onwards
• Add handlers for home, end, page up, page down and arrow left/right keys
• Use case instead of nested ifs in the openqa-revtui key handler

Follow-up of https://github.com/os-autoinst/openqa-mon/pull/157, in preparation of a Release-Candidate

[grisu48]

@ilmanzo please have a look, if you have time :slightly_smiling_face:

[ilmanzo]

Overall very good, left only a small comment for better readability :)

[ilmanzo]

Nit: would be great to avoid a screen refresh/update when the page content does not actually change.

For example when you are on the first page and press Left or page up, then the screen flickers to update itself but it's really not needed. Maybe we can just use a dirty flag to signal the Update() function it's time to redraw or not ?

func (tui *TUI) PrevPage() {
    tui.Model.mutex.Lock()
    defer tui.Model.mutex.Unlock()
    if tui.currentPage > 0 {
      tui.currentPage--
      // here we need to refresh
      tui.dirty=true
    }
}

but we can just bring this to another issue, possibly related also to #159

[grisu48]

Nit: would be great to avoid a screen refresh/update when the page content does not actually change.

For example when you are on the first page and press Left or page up, then the screen flickers to update itself but it's really not needed. Maybe we can just use a dirty flag to signal the Update() function it's time to redraw or not ?

func (tui *TUI) PrevPage() {
  tui.Model.mutex.Lock()
  defer tui.Model.mutex.Unlock()
    if tui.currentPage > 0 {
    tui.currentPage--
      // here we need to refresh
      tui.dirty=true
    }
}

but we can just bring this to another issue, possibly related also to #159

We can, but so far screen refreshes are cheap on a local terminal, so I didn't bothered much.