slightly better pasted image file names

[Robert]

Rather than using a constant+serial ("pasted_image{N}.png"), this patch uses:
1. the page name as a base (instead of 'pasted_image'), and
2. the current unix time (seconds, as hex) instead of "001", "002", "003".

The first may help if ever that image finds its way back out of zim, and complements a similar modification I made to the 'screenshot' plugin.

The second may help avoid git merge conflicts when using Zim for collaboration.

So, for example, a pasted image into the ":Bill:Clinton" page might result in "Bill-Clinton-57f7f6b2.png" rather than "pasted_image003.png".

[Jaap Karssenberg (jaap.karssenberg)]

https://github.com/jaap-karssenberg/zim-desktop-wiki/pull/60

[Launchpad Janitor (janitor)]

[Expired for Zim because there has been no activity for 60 days.]