Upload image

[terrysahaidak]

Ability to upload/capture photos directly to the room.

In the web client users has the ability to upload pictures from the clipboard by pasting it to message input.

The picture after uploading will be posted as the message with content:
[![image-alt](preview-image-url)](full-image-url)

We should add button in message input component which opens the pop-up with two options:

1. Capture picture
2. Upload from gallery

After choosing/capturing picture, we should upload it to the server and then post the message to room like described above.
While uploading, we should display linear spinner above message input or below the toolbar.

Since uploading images is a private Gitter API, we should use some another one.

[terrysahaidak]

https://github.com/marcshilling/react-native-image-picker

[terrysahaidak]

http://uploads.im/ for saving images
https://github.com/wkh237/react-native-fetch-blob for uploading from device