Add a lint indicator that replaces Brackets lint indicator

Removes default Brackets lint status indicator.
Replaces the `errorIndicator` with this `lintIndicator`.

See #61 for more detail on the reasons for this. 
Setting the `state` attribute on the element can help us change this to
``` css 
.interactive-linter-lint-indicator[status=error] {
}

.interactive-linter-lint-indicator[status=warning] {
}

.interactive-linter-lint-indicator[status=okay] {
}

.interactive-linter-lint-indicator[status=inactive] {
}
```