[libsocialcache] Allow multiple models connected to one downloader

Previously, one image downloader could only be used with one model
at a time.  This commit fixes that issue.
It also removes usage of file.map() as it would warn about mapping
greater than filesize being unsupported on some platforms.
Finally, this commit doesn't download full images until they're
requested, to save data and reduce the time it takes to load
thumbnail files by a huge factor.
Merge pull request #30 from chriadam/fixnext

[libsocialcache] Allow multiple models connected to one downloader
Bump the lib version
Merge pull request #34 from nemomobile/next

Merge next into master
[libsocialcache] Improve image downloader output path generation

Previously, the output path depended solely on the identifier passed
in for the image.  This commit adds a function which takes both an
identifier and the URL of the remote image, and uses a path generation
strategy which should result in minimal file-path collision if the
remote URL changes.
Merge pull request #36 from chriadam/fixavatars

[libsocialcache] Improve image downloader output path generation
[libsocialcache] Add support for Google calendar events

This commit allows a mapping of local event id to gcal event id
to be stored.
Merge pull request #37 from chriadam/googlecal

[libsocialcache] Add support for Google calendar events
Merge github.com:nemomobile/libsocialcache