Enhance Mono recipes

[MichalMMac]

This PR incorporates features from my MonoFramework recipes. We try to merge functionality into single set of recipes as discussed in #2.

Changes:

• Fix indent to use 2 space everywhere. 1f780a1
• We now download package using HTTPS 5afccbf
• Added CodeSignatureVerifier 81eca12
• Changed SEARCH_PATTERN and added CHANNEL variable 105f108
• Added Mono.install recipe 57da4c2

TODOs and questions:

• Please test all recipes. (I haven't tested Mono.install recipe yet)
• Do you need USER_AGENT for Mono.download? Is it there for any reason?
• Which variables do we want in all Mono recipes because they are handly for overrides? I am thinking NAME and CHANNEL.

[MichalMMac]

I've tested Mono.install.recipe. No issues.

[MichalMMac]

Hello?

[fuzzylogiq]

Michal: thanks for your very clear commits and PR. Regards: the User-Agent, there probably was a reason for it once (i.e. you didn't get to the Mac downloads without it), there isn't any more, but it isn't harming anyone so unless you're desperate to remove it, I'm leaving it in.