Update and complete the Esperanto translation

I have filled in (almost all of) the missing strings to the Esperanto file and translated them.

To clarify (chiefly for translators) some of my reverts on the fixes commited by @pizzaiolo earlier:

• Changed ‘ensaluti/elsaluti’ back to ‘saluti/adiaŭi’, because the former, in spite of its popularity, just makes no sense.
• Changed ‘etoso’ back to ‘haŭto’, because it feels more appropriate. ‘Haŭto’ concerns the visible and material (which is what themes change), while ‘etoso’ concerns general atmosphere (which is contributed to by a theme). However, either can work, so changing it back is fine with me if there's a strong preference.
• Changed ‘ŝarĝi’ back to ‘enlegi’ out of habit. The latter actually feels a bit more appropriate at times, and it's less ambiguous when it comes to grammatical objects, so I'll leave it there and will probably prefer it, but won't dwell on it either.

At any rate, neither of the three is incorrect in my book. ‘Enlegi’ is unusual, but upon analysis, yields an appropriate meaning.