WebSVN : Add option to handle "Multiview" mode

WebSVN can be configured to use Apache Multiview link format [1]. This
commit allows users to specify if this option is enabled or not in the
settings page of their WebSVN repositories.

Note that theses changes only make the option visible in the WebSVN
repos config, but does not alter the plugin's behavior. The next step
is to check the value of this option so the plugin can format WebSVN
links as appropriate.

[1] http://httpd.apache.org/docs/current/content-negotiation.html#multiviews

Fixes #46, #47

Original code was modified to use check_checked() function and fix
whitespace, commmit message reworded.

Signed-off-by: Damien Regad <damien.regad@merckgroup.com>
WebSVN: add is_multiviews method
WebSVN: added helper methods to retrieve repo info

get_websvn_url, get_websvn_name, get_websvn_path
WebSVN: differentiated URLs depending on multiviews option

The plugin is now able to handle both types of WebSVN URLs:

- standard URLs, e.g.
  http://example.com/listing.php?repname=MyRepo&path=%2Ftrunk%2F&rev=10&sc=1
- multiview URLs (introduced with 577ff7e9e56bca40d3112a1e1948de1310a32afd) like
  http://example.com/MyRepo/trunk?&rev=10

This commit restores the WebSVN functionality for sites not using the
multiviews functionality (i.e. as thigs were prior to commit
577ff7e9e56bca40d3112a1e1948de1310a32afd).

Fixes #46
WebSVN: refactoring using http_build_query
Remove if / else in url_changeset (The 'comp' operator works for both multiview and non-multiview mode)
SourceWebSVN plugin : Remove 'sc' parameters from generated links (obsolete)
SourceWebSvn plugin : fix typo
Plugin SourceWebSvn : fix 'compare' parameter (has now format 'path'@'rev')
WebSVN plugin : Fix wrong method call
Plugin SourceWebSVN : fix typo
Plugin SourceWebSVN : fix wrong comparison of SourceChangeset action field
Possible values of this field are:
'add' for file added
'rm' for file remove
'mod' for file modified
'mv' for move
SourceWebSVN plugin: Allow viewing removed files
WebSVN: minor adjustments (coding guidelines, whitespace)
WebSVN: add 'sc' option to base_url() function

The 'sc' (show change) option is obsolete since WebSVN 2.1.0 (r621)
we keep it for Compatibility with oder releases. Refer to discussion on
Github [1].

[1] https://github.com/dregad/source-integration/pull/1#commitcomment-2711137
WebSVN: multiview support and other enhancements

Fixes #46, #47