Implement Dropbox Sync

[williamstein]

https://github.com/sagemathinc/smc/blob/master/salvus/dropbox_syncer.coffee

sagemath/cloud#172

[williamstein]

This could go in the new storage daemons...

[williamstein]

This could go in the new storage daemons...

which is soon to be the old storage stuff that is deleted :-)

Dropbox Sync is rarely requested by users... and I think some who really want it just do it anyways since SMC is just a Linux user after all.

[williamstein]

Ursula Whitcher: I saw a note on GitHub that Dropbox integration is not very frequently requested, so I thought I'd let you know that it's a feature I'm currently very interested in.

[edgarcosta]

Here is a quick workaround:

1. Create a new dropbox account and share a folder with yourself (for security and practicality reasons)

2. install the daemon
   dropbox start -i

3. and stop it, by default it starts running the daemon in the background
   dropbox stop

4. Start the daemon in the foreground by doing:
   ~/.dropbox-dist/dropboxd
   and follow the instructions, i.e., copy the link.
   After everything is done, hit CTRL + C, to stop it.

5. For last do
   dropbox start
   to run the daemon in the background

[williamstein]

Closing, because Dropbox recently made a very sad decision to not support Linux (except ext4 unencrypted, which is a nonstarter). So, we will probably never support Dropbox, and instead put our effort into Google Drive integration.