Some improvements to CI

[giordano]

• Decrease frequency of TagBot to once per day
• Move FreeBSD CI to Travis, Cirrus is kind of broken
• Run Travis CI only on master, tags and a few other selected branches
• Cache artifacts in Travis and AppVeyor

[coveralls]

Coverage remained the same at 92.584% when pulling 03c5135 on giordano:mg/ci into 8458166 on JuliaGraphics:master.

[codecov]

Codecov Report

Merging #326 into master will decrease coverage by 1.14%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #326      +/-   ##
==========================================
- Coverage   92.07%   90.92%   -1.15%     
==========================================
  Files           1        1              
  Lines         454      474      +20     
==========================================
+ Hits          418      431      +13     
- Misses         36       43       +7     

Impacted Files	Coverage Δ
src/Cairo.jl	90.92% <0.00%> (-1.15%)	⬇️

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