Add function to join community profiles

[kescobo]

Add function to join community profiles

Types of changes

This PR implements the following changes: (Please tick any or all of the following that are applicable)

• [x] :sparkles: New feature (A non-breaking change which adds functionality).
• [ ] :bug: Bug fix (A non-breaking change, which fixes an issue).
• [ ] :boom: Breaking change (fix or feature that would cause existing functionality to change).

:ballot_box_with_check: Checklist

• [x] :art: The changes implemented is consistent with the julia style guide.
• [x] :blue_book: I have updated and added relevant docstrings, in a manner consistent with the documentation styleguide.
• [x] :blue_book: I have added or updated relevant user and developer manuals/documentation in docs/src/.
• [x] :ok: There are unit tests that cover the code changes I have made.
• [x] :ok: The unit tests cover my code changes AND they pass.
• [x] :pencil: I have added an entry to the [UNRELEASED] section of the manually curated CHANGELOG.md file for this repository.
• [x] :ok: All changes should be compatible with the latest stable version of Julia.
• [x] :thought_balloon: I have commented liberally for any complex pieces of internal code.

@annelle-abatoni - This should be helpful with reading in a bunch of individual metaphlan tables

julia> mss = [MicrobiomeSample("sample\$i") for i in 1:15];

julia> txs = [Taxon("taxon\$i") for i in 1:20];

julia> cm1 = CommunityProfile(spzeros(10,5), txs[1:10], mss[1:5])
CommunityProfile{Float64, Taxon, MicrobiomeSample} with 10 things in 5 places

Thing names:
taxon1, taxon2, taxon3...taxon9, taxon10

Place names:
sample1, sample2, sample3, sample4, sample5

julia> cm2 = CommunityProfile(spzeros(10,5), txs[6:15], mss[6:10])
CommunityProfile{Float64, Taxon, MicrobiomeSample} with 10 things in 5 places

Thing names:
taxon6, taxon7, taxon8...taxon14, taxon15

Place names:
sample6, sample7, sample8, sample9, sample10

julia> cm3 = CommunityProfile(spzeros(10,5), txs[11:20], mss[11:15])
CommunityProfile{Float64, Taxon, MicrobiomeSample} with 10 things in 5 places

Thing names:
taxon11, taxon12, taxon13...taxon19, taxon20

Place names:
sample11, sample12, sample13, sample14, sample15

julia> commjoin(cm1, cm2, cm3)
CommunityProfile{Float64, Taxon, MicrobiomeSample} with 20 things in 15 places

Thing names:
taxon1, taxon2, taxon3...taxon19, taxon20

Place names:
sample1, sample2, sample3...sample14, sample15

[kescobo]

This function could probably use a better name, but I'll leave it for now/