Thumbnail caching

[vishwasmittal]

Fixes #19

[vishwasmittal]

Spawns a Goroutine checks walks down the file tree, starting from the shares, and create a .fscache/thumbnails directories in each directory and creates low-resolution thumbnails for each image.

TODOs:

• [ ] Run the goroutine periodically and check the last-modified date for images and cache.

• [ ] Add a new query parameter in the /files path named as cache which will be a bool specifying whether to send the metadata with the list of files. The default will be false

[vishwasmittal]

@csoni111 @cpg the thumbnail feature is almost completed. Awaiting review. Please review it and suggest the changes.

[csoni111]

Instead of running the createThumbnailCache() func periodically, you can do this: 1) Run the createThumbnailCache()func once on program start. 2) Add a fileWatcher using fsNotify library to keep track of changing files, and update/create new thumbnails for any change in image files. Ref: https://medium.com/@skdomino/watch-this-file-watching-in-go-5b5a247cf71f

[vishwasmittal]

@csoni111 I have made the necessary changes as you asked.

[vishwasmittal]

@csoni111 please review it.