Remove unused network opcode
WHen pretty printing the OPF, do not sort the manifest items if there are comments in the manifest, as this would break the link between the comments and the content
Edit book: Have the ToC view refresh itself after any major operation on the book
Edit book: Fix replacing a file with another file with exactly the same filename causing an error. Fixes #1260822 [Cover replacement in edit fails](https://bugs.launchpad.net/calibre/+bug/1260822)
Make the error about calibre_bookmarks.txt a simple informational message
A nicer error message when a no longer existing link is activated
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Add donate entry to Help menu
Minor cosmetic fix in ebook viewer options.

Fixes #1260934 [Minor Cosmetic Bug in eBook Viewer](https://bugs.launchpad.net/calibre/+bug/1260934)
Merge branch 'master' of https://github.com/cbhaley/calibre
Edit book: Fix trying to import an html file/css file via the add new file button always resulting in a blank file
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Edit book: When syncing the position of the preview panel to the cursor
in the editor and the cursor is at or before the <body> tag set the
position of the preview panel to the top of the file, so that the top
margin of the body tag is seen easily.
Make the capitalize function re-useable
Edit book: Allow customizing which dockable windows occupy the four dock corners via Edit->Preferences. You can now also choose to have more than one row of windows in a given dock area.
Add preferences action to help menu as well
Edit book: Add options to change the default font families/sizes for the preview panel
Edit book: Fix book not being marked as modified after editing the ToC
Remove the github issue tracker, as I am tired of closing bug reports from people that dont bother to read the section on how to report bugs in the README.
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