Fix #580 - Fix false positives regarding components inside SVGs

[michalsnik]

This PR addresses the following issue #580

It does few things:

1. Stops ignoring custom components inside SVGs, so the-component will be reported now:

<template>
  <svg>
    <the-component />
  </svg>
</template>

2. Allows having SVG known elements inside the HTML namespace and not treating them as components. So for example this component (part of the SVG) will not report that circle should be PascalCase:

<template>
  <circle />
</template>
<script>
  export default {}
</script>

[ota-meshi]

@michalsnik LGTM!