General engine improvements (#437)

* Add exchange manager to engine

* Several improvements for engine and friends

1) New file.Exists func
2) gRPC TLS cert expiration date check and regeneration
3) New donation var for use across the codebase
4) Use Go log package until the logger is initialised

* Add cert tests and create dir tree if it doesn't exist for file.Write

* Link up donation address to documentation tool plus minor adjustments

* Fix remaining donation addrs

* Move non-needed reload exchange funcs

* Revert accidental config_example.json changes 🕯️

* Use go logger for logging until the logger has initiliased, otherwise no output will be seen

* Link up portfolio delay val and other fixes

* Run go mod tidy after dependabot PR

* Address nitterinos

CONTRIBUTORS

@@ -5,6 +5,7 @@ shazbert | https://github.com/shazbert
 gloriousCode | https://github.com/gloriousCode
 xtda | https://github.com/xtda
 ermalguni | https://github.com/ermalguni
+dependabot-preview[bot] | https://github.com/apps/dependabot-preview
 vadimzhukck | https://github.com/vadimzhukck
 140am | https://github.com/140am
 marcofranssen | https://github.com/marcofranssen
@@ -14,6 +15,7 @@ crackcomm | https://github.com/crackcomm
 andreygrehov | https://github.com/andreygrehov
 bretep | https://github.com/bretep
 woshidama323 | https://github.com/woshidama323
+vazha | https://github.com/vazha
 gam-phon | https://github.com/gam-phon
 cornelk | https://github.com/cornelk
 if1live | https://github.com/if1live
@@ -21,18 +23,19 @@ lozdog245 | https://github.com/lozdog245
 soxipy | https://github.com/soxipy
 herenow | https://github.com/herenow
 blombard | https://github.com/blombard
+Christian-Achilli | https://github.com/Christian-Achilli
 CodeLingoBot | https://github.com/CodeLingoBot
 CodeLingoTeam | https://github.com/CodeLingoTeam
 Daanikus | https://github.com/Daanikus
 daniel-cohen | https://github.com/daniel-cohen
 DirectX | https://github.com/DirectX
 frankzougc | https://github.com/frankzougc
-starit | https://github.com/starit
-Jimexist | https://github.com/Jimexist
-lookfirst | https://github.com/lookfirst
 idoall | https://github.com/idoall
 mattkanwisher | https://github.com/mattkanwisher
 mKurrels | https://github.com/mKurrels
 m1kola | https://github.com/m1kola
 cavapoo2 | https://github.com/cavapoo2
 zeldrinn | https://github.com/zeldrinn
+starit | https://github.com/starit
+Jimexist | https://github.com/Jimexist
+lookfirst | https://github.com/lookfirst