sf_fs: Improve default FS determination and make FS type optional

sf_create_fs: Make FS type optional (defaults to value returned by sf_fs_default_type())
sf_fs_default_type: Search ext4/3/2
Add sf_lvm_vg_free() function
sf_check_line: Modify info message
sf_lvm: Minor fixes

sf_lv_to_vg: fix
sf_lvm_vg_free; Typo fix
sf_fs.sh: Deprecate functions not starting with 'sf_fs_' prefix

Rename every functions in this file to start with 'sf_fs_'.
Also improve function names
Change arg order in new function sf_fs_create_lv_fs to make FS type optional
Switch version to 1.26.0
Merge branch 'release_1.26.0' into develop