Add documentation on FmModule stuff, it appear to be not documented.
Extra custom items for FmFolderModel.

The commit adds APIs fm_folder_model_extra_file_add() and
fm_folder_model_extra_file_remove() which add and remove some custom
FmFileInfo item into FmFolderModel. Those items aren't counted as
items from FmFolder associated with the model and will be not removed
if FmFolder is replaced. New items can be inserted into the model by
different ways:
- before all items of the FmFolder;
- mixed into items of the FmFolder by sorting rules;
- after all items of the FmFolder.
Save option 'drop_default_action' in more portable way.

If we save the option not as enum number but as text then it will be
well portable and safe if the enum will be changed sometime.
Document versions of appearance of new members of FmConfig structure.
New module: gtk_file_prop:inode/x-shortcut, it supports Type=Link desktop files.

The icon, name, and hidden attributes are currently supported to edit.
Item LinkTo belongs to PCManFM and SendTo is rather a category.

The Link item is similar to CopyTo or MoveTo and therefore better to be in PCManFM.
The "Send to" is a category which is already present in meny as AddBookmark or
Compress. It is better to just allow extensions to add items there instead.
Since both those items were never implemented, this commit just removes unused text.
Add MoveCategory and SendToCategory placeholders info FmFileMenu.

The AddBookmark and Compress moved into SendToCategory where they belongs.
Show context menu for folders in FmDirTreeView sidebar.

It is implemented as simple version of standard FmFileMenu with
elements such as Copy/Cut/Del removed from the menu.
[#3598836]Place columns of Compact View in right-to-left order for RTL locales.
New APIs fm_hide_file() and fm_unhide_file()

New APIs just send a job to change "hidden" file attribute.
Add "hidden" attribute support info file properties dialog.

The new support adds a check button on bottom of "Permissions" tab.
The button is unchangeable if file doesn't support the change.
Tooltips are updated accordingly.
Correct "hidden" attribute for native desktop entry files.

It was set if file is dot-file but for desktop entries the "Hidden" key
should be checked as well.
Item 'Hide'/'Unhide' in MoveCategory of FmFileMenu if FS supports it.

If file system can change file attribute "hidden" then it is reasonable
to have the element in the file context menu as well.
Options 'SortIgnoreCase' and 'MingleDirs' for folder context menu.
Commit from LXDE Pootle server by user KlemenKosir.: 303 of 352 strings translated (12 fuzzy).
Merge remote-tracking branch 'upstream'