Mark various CLI strings for translation
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Allow users to add extra mimetype icons by placing appropriately named image files in the resources/mimetypes override directory
Fix allow_user_override not working for I() and also fix allow_user_override not working with different values for the same path.
oops
Refactor various ebook download functions

The functions are now easily testable individually. An extra HTTP connection
when downloading a file from a URL directly is avoided. A workaround for
Project Gutenberg refusing to serve ebook files to browsers is added.
See #1354735 (When using "Get Books," all downloaded Project Gutenberg ePub books (and only Pr. Gut. books) are .2 MB, that is, they show up in my Calibre library, but they are empty. This wasn't so before as I have downloaded many Pr. Gut. ePub books in the past using “Get Books.” I have updated Calibre versions twice since this problem began. ePub downloads through other providers (eg., Feedbooks, Legimi, MobileRead) using “Get Books” functions correctly. Mac OS 10.7.5, Calibre 1.48.0.) [When using "Get Books," all downloaded Project Gutenberg ePub books (and only Pr. Gut. books) are .2 MB, that is, they show up in my Calibre library, but they are empty. This wasn't so before as I have downloaded many Pr. Gut. ePub books in the past using “Get Books.” I have updated Calibre versions twice since this problem began. ePub downloads through other providers (eg., Feedbooks, Legimi, MobileRead) using “Get Books” functions correctly. Mac OS 10.7.5, Calibre 1.48.0.](https://bugs.launchpad.net/calibre/+bug/1354735)
Update Heraldo de Aragon
Add a link to the editor video tour in the User Manual
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Simplify code to show GUI debug log

Fixes regression caused by Qt 5 behavior change that prevented the
debug log from being displayed in linux.
Workaround for bug in Qt 5 that causes crashes if QDesktopServices is used before constructing a QApplication
Abort terminal save on error instead of quitting editor
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PDF Output: Fix balanced parentheses in the text of items in the Table of Contents not being rendered properly by some PDF viewers. Fixes #1358443 [PDF ToC omitting entries in parentheses](https://bugs.launchpad.net/calibre/+bug/1358443)
E-book viewer: Remove extra spacing between document and scrollbars.  This is particularly noticeable when using a dark theme for the viewer.
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Edit Book: Make the edit saved search/add saved search popup window non-modal. Fixes #1354785 [The "Edit Search" window blocks interaction with the ebook-editor main window](https://bugs.launchpad.net/calibre/+bug/1354785)
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Update Down to Earth
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