Build scripts cleanup and dictionary loading optimization

* moved the source languages out of assets/ into their own directory (#356)
  
  * split build.gradle into several smaller files

  * improved word frequency validation during build time

  * slightly optimized dictionary loading speed using pre-calculated file size

  * fixed a potential crash when loading invalid assets

  * fixed dictionary loading progress starting at 100% then jumping to 0% when manually loading two dictionaries one after another

  * documentation update

languages/definitions/Greek.yml

@@ -0,0 +1,14 @@
+---
+locale: el-GR
+dictionaryFile: gr-utf8.csv
+layout:
+  - [SPECIAL] # 0
+  - [PUNCTUATION_FR] # 1
+  - [α, β, γ, ά] # 2
+  - [δ, ε, ζ, έ] # 3
+  - [η, θ, ι, ή, ί, ϊ, ΐ] # 4
+  - [κ, λ, μ] # 5
+  - [ν, ξ, ο, ό] # 6
+  - [π, ρ, σ, ς] # 7
+  - [τ, υ, φ, ύ, ϋ, ΰ] # 8
+  - [χ, ψ, ω, ώ] # 9