Use default values for scheme and template list URLs

[lhanson]

Rather than require the explicit inclusion of SchemesMasterURL and TemplatesMasterURL in the configuration, default to the usual values if not present.

Closes #30

[codecov[bot]]

Codecov Report

Merging #32 into master will increase coverage by 4.15%. The diff coverage is 80%.

@@            Coverage Diff             @@
##           master      #32      +/-   ##
==========================================
+ Coverage     8.3%   12.46%   +4.15%     
==========================================
  Files           5        5              
  Lines         349      353       +4     
==========================================
+ Hits           29       44      +15     
+ Misses        315      302      -13     
- Partials        5        7       +2

Impacted Files	Coverage Δ
main.go	1.29% <0%> (ø)	:arrow_up:
config.go	44.11% <100%> (+44.11%)	:arrow_up:

---

Continue to review full report at Codecov.

Legend - Click here to learn more Δ = absolute <relative> (impact), ø = not affected, ? = missing data Powered by Codecov. Last update fab0339...109eb0c. Read the comment docs.

[pinpox]

Thanks!