Reference function from object to ensure context
Reference function from object to ensure context

When `updateLastAccessed` is used as a callback in `chrome.tabs.query`,
the context will not be correct. Always reference from the owning
object, `TabManager`, to ensure correct context.

Fixes PR #154
jacobSingh/tabwrangler,tabwrangler/tabwrangler,tabwrangler/tabwrangler,tabwrangler/tabwrangler,jacobSingh/tabwrangler