Folder/namespace renaming

[emteknetnz]

Should do this close to the conclusion of the feature dev so as not to cause any merge conflicts with open PRs

ACs

• Move contents of Extension folder to the Extensions folder and ensure namespace matches
• Pluralise the following folders/namespaces to match the other folders - FormField, Job, Model, Service
• Create Controllers folder, move LoginSessionController there, update namespace from /Control/ to /Controllers/
• LoginSessionController - change class it extends from LeftAndMain to Controller, remove $ignore_menuitem config
• Change LoginSessionMiddleware namespace from /Control/ to /Middleware/
• Double check all other namespaces match folders
• Remove unused class SilverStripe\SessionManager\Forms\GridFieldRevokeLoginSessionAction

PRs

• ENH Update folders + namespaces, remove unused class #74

[maxime-rainville]

I've added an AC to remove the unused class SilverStripe\SessionManager\Forms\GridFieldRevokeLoginSessionAction