script for bucket creation and priv setting

Getting the policy right on an s3 bucket is twiddly. Make a script to make sure it gets set correctly. Something to being with:
```
{
"Version": "2012-10-17",
"Statement": [
{
"Sid": "AddPerm",
"Effect": "Allow",
"Principal": "*",
"Action": "s3:GetObject",
"Resource": "arn:aws:s3:::testing.higlass.gehlenborglab.org/*"
},
{
"Sid": "AddPerm",
"Effect": "Allow",
"Principal": "*",
"Action": "s3:ListBucket",
"Resource": "arn:aws:s3:::testing.higlass.gehlenborglab.org"
},
{
"Sid": "AddPerm",
"Effect": "Allow",
"Principal": "*",
"Action": "s3:PutObject",
"Resource": "arn:aws:s3:::testing.higlass.gehlenborglab.org/*"
}
]
}
```
... but it shouldn't be world writable in the long run.