PHP code sniffer autofixes

Automatic coding style fixes

fix: resolve conflict of type\Page and meta\Page

These two classes having the same name caused an error that on some
pages, after saving the page, the page itself remained blank.
The error-log conta

fix: resolve conflict of type\Page and meta\Page

These two classes having the same name caused an error that on some
pages, after saving the page, the page itself remained blank.
The error-log contained the following:

[Mon Nov 28 09:05:52 2016] [error] [client 91.65.183.141] PHP Fatal
error: Cannot use dokuwiki\\plugin\\struct\\types\\Page as Page because
the name is already in use in
[...]/lib/plugins/struct/meta/Search.php on line 7,
referer: [...]

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fixed problem with multicolumns and made the param name clearer

make label part of Page column

only allow Page types for PageColumn

correctly dynamically filter %title% column #132

introduce getColName vs. getFullColName

Fix sorting by a multi column

A multicolumn is always sorted by its first value which is already copied
to the respective column in the table.

SPR-466

Use DokuWiki new autoloader for class files

No longer do we need to register our own autoloader. Namespace had to be
vendor prefixed.

let PageColumns always have the same fq label

make sure page columns have a label

fixed getColName to contain the data_ prefix

Added a few more guarding exceptions. We want things to break early
instead of having debugging headaches later

streamlined PageColumn handling

introduced a method that returns the full column name. It can always be
called - on Column and PageColumn

added support for selecting the PageID