Templates: Add possibility to overwrite HTML templates from Base Modules in Template modules.

[AntonLV]

Try to realize the same possibility for CSS classes.

[AntonLV]

HTML files in modules with <bx_include_base: /> should be removed to allow Template engine to search in Custom template -> Base Modules -> Base System.
For example, modules/boonex/persons/template/cover.html file with the following content:

<bx_include_base:../modules/base/profile/template/cover.html />

[AntonLV]

1. Empty CSS files in modules can be removed, like modules/boonex/persons/templates/css/main.css, which just includes the parent CSS file from Base Profile module using @import instruction.
2. @import instructions isn't needed in module's CSS files anymore. For example, modules/boonex/persons/templates/css/main.css CSS file may not use the code @import url(../../../../base/profile/template/css/main.css); to include CSS file from parent Base module because parent CSS file will be added automatically when BxDolModuleTemplate::addCss('main.css') code is used.

Note: If 1 and 2 won't be done, CSS files referenced from Base modules, like base/general/template/css/main.css, will be included a number of times and prevent the correct work of 'overwrite in template' feature.

Check process for Text based module: Template:[[module's folder]/css] -> Template:[mod_text/css] -> Template:[mod_general/css] -> Template:[system/css folder] -> Core:[[module's folder]/template/css] -> Core:[base/text/template/css] -> Core:[base/general/template/css] -> Core:[template/css].

[AntonLV]

Check process was changed. First of all system checks in module related locations (in template, in core), then it checkes in system locations (in template, in core). This approach is more close to initial one.
Check process for Text based module:

1. Check in module related locations: Template:[[module's folder]/css] -> Template:[mod_text/css] -> Template:[mod_general/css] -> Core:[[module's folder]/template/css] -> Core:[base/text/template/css] -> Core:[base/general/template/css]
2. Check it system locations: Template:[system/css folder] -> Core:[template/css].