IE rendering engine fix (meta header)
IE rendering engine fix (meta header)

# Changes overview

## renderer.php

### Add meta header for Internet Explorer

In the Internet Explorer the slideshow does render but navigation is
impossible. No keyboard shortcut is working. It turns out, that the IE11
was using the compatibility mode IE7 - maybe because of intranet
policies. Adding `<meta http-equiv="X-UA-Compatible" content="IE=edge"
/>` to the header fixes the problem.

### Fix some method signatures because of debug warnings

> Warning: Declaration of renderer_plugin_revealjs::table_open($maxcols
= NULL, $numrows = NULL, $pos = NULL) should be compatible with
Doku_Renderer_xhtml::table_open($maxcols = NULL, $numrows = NULL, $pos =
NULL, $classes = NULL) in <snip>plugins\revealjs\renderer.php on line
424

Added param `$classes = NULL` to the follwing methods

- table_open
- tablerow_open
- tableheader_open
- tablecell_open

### Cleanup mixed usage of tabs and spaces

neuralyzer/dokuwiki-plugin-revealjs,ogobrecht/dokuwiki-plugin-revealjs,ogobrecht/dokuwiki-plugin-revealjs,ogobrecht/dokuwiki-plugin-revealjs,neuralyzer/dokuwiki-plugin-revealjs,neuralyzer/dokuwiki-plugin-revealjs