* Refactor entry to GReader API format
Some code was copied in two locations and not completely uniform.
Cleaning of related variables and functions (e.g. better types for entries and categories as objects vs. as IDs).
Usecase: I need to call the same GReader-compatible serialization from an extension
* Fixed some edge cases
* Keep summary instead of content
`summary` and `content` seems to be used interchangeably in the Google Reader API. We have been using `summary` for our client API and `content` in our export/import, so stick to that.
* Use typographic quotes
* A few fixes
* Fix
* Fix not saved
* Implement feedback
* Detail
* Revert spoken English fixes
Left for a future dedicated discussion
* More reverts
* Final reverts
* Final minor
Even if the issue #3035 seemed pretty simple at a first glance, it was
more complicated than I expected. Because we send CSP headers AFTER
running the controller actions, it means we can't "echo" any content
from the controller. It's in fact a good practice, but it was easier at
the time we developed the feature.
To fix that, the only thing I had to do was to move the `print()` and
`readfile()` function into the view. The problem was that we needed to
output the content from the CLI too. Then, things became more
complicated. I decided to extract the export-related methods in a
`FreshRSS_Export_Service` class, in order to use it from both the
controller and the CLI. It was an opportunity to refactor the whole
feature in order to make it a bit more linear and easy to read.
Reference: https://github.com/FreshRSS/FreshRSS/issues/3035
