remove deleted files on update of extension

Resolves #1192

`/lib/plugins/<plugin>/deleted.files`
which list files that can be removed e.g.
```
# This is a list of files that were present in previou

remove deleted files on update of extension

Resolves #1192

`/lib/plugins/<plugin>/deleted.files`
which list files that can be removed e.g.
```
# This is a list of files that were present in previous plugin releases
# but were removed later. An up to date plugin should not have any of
# the files installed
action.php
folder/file.txt
```

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translation update

fixed a few links and html errors in language files

fixed occurrences of html named entities in translation files to be xhtml-compatible

fixed lots of missing format strings in language files

changed all input type=submit buttons to button type=submit button for better stylability

translation update

translation update

translation update

Update lang.php

Выравнивание и разбиение по образцу en/lang.php, унификация "директорий" и "папок", "расширений" и "дополнений"

fixed small spacing/alignment issues in display options of extension manager

fixed installed extensions in extension manager not displaying without JS

translation update

translation update

translation update

translation update

fixed isBundled() check when remote info is unavailable

translation update

update test groups for the extension manager test

added composer setup and the first composer package php-archive

translation update

Adhere to CSS style guide

Add class name using tab name

Change ID name

translation update