Rename Namespaces, use Globals

[Romazes]

Description

1. Rename namespace QuantConnect.IQFeed -> QuantConnect.DataSource.IQFeed
2. Rename: DataQueueHandler -> DataProvider
3. Use Globals for credentials access for subscription validation.
   This follows Consolidate Configuration.Get usages Lean#7796
4. Handle history provider returning null
   This follows Handle history provider returning null Lean#7804
5. Handle data downloader provider returning null
   This follows feat: downloader data provider returning null Lean#7812

Related Issue

N/A

Motivation and Context

It keeps unify format like in another Data Sources.

Requires Documentation Change

N/A

How Has This Been Tested?

N/A

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• Refactor (non-breaking change which improves implementation)
• Performance (non-breaking change which improves performance. Please add associated performance test and results)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Non-functional change (xml comments/documentation/etc)

Checklist:

• My code follows the code style of this project.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.
• My branch follows the naming convention bug-<issue#>-<description> or feature-<issue#>-<description>

[jhonabreul]

Thanks! Leaving some comments