Fix post settings photo popover position

Popover is now well centered after rotation
Set post settings tableview as grouped
Prime the share activity when its safe.

Avoid a visible performance hit later if scrolling.
Updates no results view.

Shows "Fetching posts..." status and fixes an issue with the no posts message flickering briefly.
show reblogg button even when sharing_enabled is false
Post setting popover cleanup
If there is no image for the button, return nil.
White space and code style corrections.
Removing duplicated image gen code and using pre existing category.
Remove post settings tableview without extra padding

Plus added a taxonomy localized string to the first section header
Fixing warning because of unused variable in ReaderPostsViewController
Merge pull request #2094 from wordpress-mobile/issue/fix-warning-because-of-unused-variable

Fixing warning because of unused variable in ReaderPostsViewController
Merge pull request #2089 from wordpress-mobile/issues/1765-blue-dot

If there is no image for the button, return nil.
Merge pull request #2093 from wordpress-mobile/issue/adjust-tab-bar-background-to-use-pre-existing-method

Removing duplicated image generation code and using pre existing category.
Merge pull request #2021 from wordpress-mobile/issues/1650-prevent-scrolling-lag-when-sharing

Prime the share activity when its safe.
Merge pull request #2009 from cyrilchandelier/issues/1918-popover-position

Fix post settings photo popover position
Merge pull request #2012 from cyrilchandelier/issues/1917-post-settings-headers

Set post settings tableview as grouped
Merge pull request #2069 from davidfilip/issues/2051-reblogging-allowed-all-time

Allow reblogging when `share_enabled` is false.
Updated a comment in PostSettingsViewController.m
Merge branch 'develop' of github.com:wordpress-mobile/WordPress-iOS into issues/1663-animated-paper-issue

Conflicts:
	WordPress/Classes/ViewRelated/Reader/ReaderPostsViewController.m