Added regular expressions to validate table and container names

[Aaronontheweb]

Help prevent the user from running into a runtime issue with Azure Table or Blob storage by validating the names of containers and tables before we fire up the plugin:

https://blogs.msdn.microsoft.com/jmstall/2014/06/12/azure-storage-naming-rules/

Tables

Name of the table
Table names must conform to these rules:

Table names must be unique within an account.
Table names may contain only alphanumeric characters.
Table names cannot begin with a numeric character.
Table names are case-insensitive.
Table names must be from 3 to 63 characters long.
Some table names are reserved, including "tables". Attempting to create a table with a reserved table name returns error code 404 (Bad Request).
These rules are also described by the regular expression "^[A-Za-z][A-Za-z0-9]{2,62}$".

Table names preserve the case with which they were created, but are case-insensitive when used.

Blobs

A container name must be a valid DNS name, conforming to the following naming rules:

Container names must start with a letter or number, and can contain only letters, numbers, and the dash (-) character.
Every dash (-) character must be immediately preceded and followed by a letter or number; consecutive dashes are not permitted in container names.
All letters in a container name must be lowercase.
Container names must be from 3 through 63 characters long.

[Aaronontheweb]

closed via #21