Move LZ arrows into dashboard

[pjvandehaar]

New components for the dashboard: (docs src)

(on left)

• [x] Go to Manhattan Plot
• [x] chr:start-end

(in middle)

• [x] Far left, left
• [x] zoom in/out (just a big +/-)
  • see zoom_region
• [x] right, far right
  • see shift_region

(on right)

• download

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• [x] allow centering of components

  .lz-dashboard.lz-plot-dashboard { text-align: center; padding-bottom: 0; }
  .lz-dashboard-left, .lz-dashboard-right { display: inline-block; }
  // for now:
  .lz-dashboard-group-start, .lz-dashboard-group-middle, .lz-dashboard-group-end { float: none !important; }
  // later:
  .lz-dashboard-center { float: none !important; }
  // and apply [.lz-dashboard-left, -right] attributes to -center

  removing float breaks the partial-occlusion of buttons behind the svg b/c it makes the parent actually contain the component-divs, which seems to make their padding take effect.

  also, text-align: center cascades down to children, affecting their html.

[pjvandehaar]

It works but is gross. I'll hopefully merge position: "center" for components into LZ sometime.