Locally saved posts

[flipdp]

Not sure if this fits in the official repo. I created this because I was annoyed with the lack of features of saved posts.

I just hacked this together from the History so the code may need to be cleaned up a bit.
The LocalSave class is entirely static because that was the fastest way I could think of to add History and Saved post caching,
but it can probably almost entirely be moved into LocalPostPagingSource and made non-static.

All the features I added ( if I didn't forget anything ):

• Added locally saved posts to bypass the default limit of 1000 saved posts.
• Added the ability to sort locally saved posts by random, added-date and upload-date.
• Added the ability to filter by title, subreddit, flair and tags that can be added to locally saved posts.
• Locally saved posts can be backed up in json files.
• History and Saved posts can be cached and bulk added to the locally saved posts.
• Local posts can be accessed from the navigation bar above History.
• Posts can be saved by long pressing on the bookmark icon or in the share menu.
• Tags can be edited from the share menu.
• Multiple search filters can be applied by separating keywords by whitespaces and using underscores in place of spaces in keywords. It will find posts matching any keyword.

[flipdp]

this line can also be removed. doesnt actually do anything

[Docile-Alligator]

Thank you for your PR. I will look at this after the Reddit API things settle down.

[Humorist2601]

Hello, any update on this? This PR alongwith #1282 will allow seeing of post history in Anonymous mode so that we can hopefully get marking posts as read in that mode. Thanks