Embed assets in elf file (#2466)

* FBT: file_assets generator
* Elf file: process manifest section externally
* FBT, file_assets generator: add assets signature
* Storage: assets path alias
* Flipper application: assets unpacker
* Apps, Storage: use '/data' alias for apps data
* Storage: copy file to file
* Assets: log flag, fixes
* Update f18 api
* Assets: asserts
* Assets: fix signature_data check
* App assets: example
* Example assets: fix folder structure in readme
* Assets: fix error handling
* Assets builder: use ansii instead of utf-8, use .fapassets section instead of .fapfiles, add assets path to signature
* Elf file: comment strange places
* Storage: totaly optimized storage_file_copy_to_file

applications/examples/example_apps_assets/files/poems/my shadow.txt

@@ -0,0 +1,23 @@
+My Shadow by Robert Louis Stevenson
+
+I have a little shadow that goes in and out with me,
+And what can be the use of him is more than I can see.
+He is very, very like me from the heels up to the head;
+And I see him jump before me, when I jump into my bed.
+
+The funniest thing about him is the way he likes to grow—
+Not at all like proper children, which is always very slow;
+For he sometimes shoots up taller like an India-rubber ball,
+And he sometimes gets so little that there’s none of him at all.
+
+He hasn’t got a notion of how children ought to play,
+And can only make a fool of me in every sort of way.
+He stays so close beside me, he’s a coward you can see;
+I’d think shame to stick to nursie as that shadow sticks to me!
+
+One morning, very early, before the sun was up,
+I rose and found the shining dew on every buttercup;
+But my lazy little shadow, like an arrant sleepy-head,
+Had stayed at home behind me and was fast asleep in bed.
+
+source: "https://poets.org/anthology/poems-your-poetry-project-public-domain"