Add CAP-85 - Externally managed contract executables (#1973)

* Add CAP-85 - Externally managed contract executables

* typo fixes

* !fixup specify that executable reference must be persistent and add a small spec section for the classic op update

* !fixup rename owner field in XDR for clarity

* Clarify the update system event semantics

* !fixup minor fixes

* !fixup more minor fixes

Author: dmkozh

core/README.md

@@ -118,6 +118,7 @@
 | [CAP-0060](cap-0060.md) | Update to Wasmi register machine| Graydon Hoare | Accepted |
 | [CAP-0072](cap-0072.md) | Contract signers for Stellar accounts | Dmytro Kozhevin | Draft |
 | [CAP-0084](cap-0084.md) | Muxed Contract Addresses | Jake Urban | Draft |
+| [CAP-0085](cap-0085.md) | Externally managed contract executables | Dmytro Kozhevin | Draft |
 
 ### Rejected Proposals
 | Number | Title | Author | Status |