Improve performance of network graph

Created by: hiroponz

I think that loading network graph is as fast as that of 5.0.

Overview

1. Rendering graph partially.
2. Reduce database access to get notes.
3. Enable vertical scrolling.Thanks @giggsey.
4. Some minor bugs related to network graph is fixed.

Dragging network graph is disabled, because it conflicts with scroll.

Screenshot

fixes #3684 (closed) refs #3711

Created by: coveralls

Coverage decreased (-0.17%) when pulling 05c2c15c on hiroponz:improve-performance-of-network-graph into 75fbdc40 on gitlabhq:master.

By Administrator on 2013-04-25T21:32:21 (imported from GitLab project)

By Administrator on 2013-04-25T21:32:21 (imported from GitLab)

Created by: coveralls

Coverage decreased (-12.24%) when pulling 1ae9c697 on hiroponz:improve-performance-of-network-graph into 75fbdc40 on gitlabhq:master.

By Administrator on 2013-04-25T22:31:41 (imported from GitLab project)

By Administrator on 2013-04-25T22:31:41 (imported from GitLab)

Created by: dzaporozhets

Thanks!

By Administrator on 2013-04-26T07:05:37 (imported from GitLab project)

By Administrator on 2013-04-26T07:05:37 (imported from GitLab)

Created by: hiroponz

@randx @giggsey I have found that it is broken completely if displayed by Win7 IE9. But I have no idea to fix this. Should I revert the vertical scroll feature?

Changing "Compatibility View settings" seems to improve the problem.

BTW some oter pages are also broken if displayed by Win7 IE9.

By Administrator on 2013-04-26T10:53:35 (imported from GitLab project)

By Administrator on 2013-04-26T10:53:35 (imported from GitLab)

Created by: hiroponz

I think that it is same with #1842 (closed).

By Administrator on 2013-04-26T12:07:45 (imported from GitLab project)

By Administrator on 2013-04-26T12:07:45 (imported from GitLab)

Created by: giggsey

I know this has been merged, but I've just tried 5.2, and I like the scrolling.

However, the cross 'move' cursor doesn't work if you can't drag it around. I think it should be changed back to default.

By Administrator on 2013-05-20T15:10:24 (imported from GitLab project)

By Administrator on 2013-05-20T15:10:24 (imported from GitLab)

Created by: hiroponz

@giggsey Please review my PR.

By Administrator on 2013-05-21T00:29:54 (imported from GitLab project)

By Administrator on 2013-05-21T00:29:54 (imported from GitLab)