Let users supply their own tools signature files

Related to #220. Solve this only after #220.

Related to #221, #222, #223, #224, #225. Solve them together or close one after another. Share design decisions - uniform solutions.

Let users supply their own tools (compilers, packers, installers) signature files.

Right now, RetDec tools use only signatures from `support/yara_patterns/tools` to identify known tools.

Probably refactor the whole system in the process:
- Refactor the directory structure. Something like share/retdec/support/tools-patterns/.
- Let users specify their own pattern file(s) or whole directory(s) through `retdec-decompiler.sh` script parameter. Specified files can be both text YARA and compiled YARA rules.
- Let users add their files to the user support directory (e.g. something like share/retdec/user-support/tools-patterns). These will be always used, without user needing to specify them via script parameters.
- Write a how-to wiki page. Encourage users to contribute their signatures to upstream.

Start by reading #220 and the related issues #221-#224, since this issue requires shared design decisions. Inspect support/yara_patterns/tools and retdec-decompiler.sh, then define the directory and parameter changes described here. Done means user-supplied text or compiled signatures, user-support patterns, and a how-to wiki page are supported together.

Written by the indexing model from the issue text.